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Electromagnetic radiation, Light–Reflection and Refraction, Mirror- Lens [ Physics] [ Science Set 12]| UPPSC Prelims PYQ of Last 30 Years |Important Objective Question Answer, MCQ and QUIZ

 1. Diffusion of light in the atmosphere takes place due to ( UPPSC PYQ 2021)

a) Carbon dioxide

b) Dust particles

c) Helium

d) Water vapors

Answer. b) Dust particles;

The diffusion of light in the Earth's atmosphere is primarily responsible for the blue color of the sky during the day. This phenomenon, known as Rayleigh scattering, occurs when shorter wavelengths of light, such as blue and violet, are scattered in all directions by tiny dust particles and molecules in the atmosphere. Blue light is scattered more than other colors due to its shorter wavelength, which is why we see a blue sky.

Additionally, during sunrise and sunset, when the sun is near the horizon, its light has to pass through a larger portion of the atmosphere. This increased path length scatters the shorter wavelengths even more, allowing the longer wavelengths, such as red and orange, to dominate the sky's colors, creating the beautiful hues seen during these times.

2. Which of the following types of glass can cut off ultraviolet rays? ( UPPSC PYQ 2021)

a) Soda glass

b) Pyrex glass

c) Jena glass

d) Crookes glass

Answer. d) Crookes glass can be cut off ultraviolet rays. 

Glass is a highly cold liquid.

A type of glass known as "UV-filtering glass" or "UV-blocking glass" or Crookes glass is designed to cut off or block ultraviolet (UV) rays. These types of glass are specially treated or coated to absorb or reflect UV radiation, helping to protect the interior of buildings, cars, or other spaces from UV damage and reducing the risk of UV-related health issues.

Crookes glass is commonly used in windows, eyeglasses, and sunglasses to provide UV protection for both objects and people. It helps to reduce the harmful effects of UV rays, such as fading of fabrics and artwork, as well as the risk of skin and eye damage from prolonged exposure to UV radiation. This type of glass is particularly important in environments where UV protection is necessary, such as in healthcare settings, museums, and automotive applications.

3. Sunglasses are made up of glass?

a) Soda glass

b) Pyrex glass

c) Jena glass

d) Crookes glass

Answer. d) Crookes glass;

Crooks glass mainly comprises cerium oxide, which absorbs the ultraviolet radiations from the sun

Soda Glass: Soda-lime glass, often referred to as soda glass, is a common type of glass composed of silica, soda (sodium oxide), and lime (calcium oxide). It's widely used for making bottles, containers, windows, and everyday glassware. It's relatively inexpensive and has good optical clarity but is not particularly resistant to high temperatures or thermal shock.

Pyrex Glass: Pyrex is a brand of borosilicate glass, known for its high resistance to heat and thermal shock. It's commonly used for cookware like baking dishes and laboratory glassware due to its ability to withstand rapid temperature changes without shattering.

4. Mirage formations are an example of- ( UPPSC PYQ)

a) Refraction

b) Diffraction

c) Total internal reflection

d) Dispersion

Answer. c) Total internal reflection;

Refraction: Refraction occurs when light passes from one medium (such as air) into another medium with a different optical density (such as glass or water). This change in optical density causes the light to change its direction or bend. Refraction is responsible for phenomena like the bending of a pencil in a glass of water and the formation of rainbows.

Diffraction: Diffraction is the bending or spreading of light waves as they encounter an obstacle or aperture. This phenomenon occurs when light waves encounter an obstruction or aperture that is on the order of the wavelength of the light. Diffraction is responsible for effects like the spreading of light around the edges of an obstacle and is essential in understanding how light behaves when it encounters small openings or slits.

Total Internal Reflection: Total internal reflection occurs when light traveling in a denser medium (e.g., glass) strikes the boundary with a less dense medium (e.g., air) at an angle greater than the critical angle. Instead of passing through, the light reflects entirely back into the denser medium. This phenomenon is the basis for optical fiber communication, where light can be transmitted through a fiber by repeatedly undergoing total internal reflection.

Dispersion: Dispersion refers to the separation of white light into its constituent colors (spectrum) when it passes through a medium like a prism or a water droplet. This separation occurs because different colors of light have different wavelengths, and they bend by varying amounts when they pass through the medium. Dispersion is responsible for the rainbow's formation when sunlight is refracted and dispersed by raindrops in the atmosphere.

5. A Black body does NOT ( UPPSC PYQ)

a) Emit radiation

b) Absorb radiation

c) Refract radiation

d) None of the above

Answer. a) Emit radiation

6. A soap bubble seen under white light shows color. The phenomenon responsible for this is as follows? ( UPPSC PYQ)

a) Scattering

b) Interference

c) Dispersion

d) Diffraction

Answer. b) Interference;

Scattering: Scattering is the process by which light changes its direction when it interacts with particles or irregularities in a medium. There are different types of scattering, including Rayleigh scattering (responsible for the blue color of the sky), Mie scattering (associated with larger particles), and Raleigh-Gans-Debye scattering (applicable to a range of particle sizes). Scattering can occur in various directions, leading to the diffusion of light.

Interference: Interference occurs when two or more waves overlap and combine, leading to the reinforcement (constructive interference) or cancellation (destructive interference) of certain parts of the waves. In optics, this can result in patterns of bright and dark regions, such as those seen in interference fringes produced by double-slit experiments or thin film interference.

Dispersion: Dispersion refers to the separation of white light into its constituent colors (spectrum) when it passes through a medium like a prism or a water droplet. This separation occurs because different colors of light have different wavelengths and refract by varying amounts when passing through the medium. Dispersion is responsible for the rainbow's formation and is crucial in optical systems that use prisms to analyze or separate light.

Diffraction: Diffraction is the bending or spreading of light waves as they encounter an obstacle or aperture, typically when the size of the obstacle or aperture is on the order of the wavelength of light. Diffraction patterns can result in distinctive patterns of light and dark regions. Diffraction plays a role in phenomena like the spreading of light around the edges of an obstacle, as seen in single-slit and double-slit experiments.

7. In a Sitar, which type of sound vibrations are produced?

a) Progressive and Longitudinal

b) Progressive and Transverse

c) Stationery and Longitudinal

d) Stationery and Transverse

Answer. d) Stationery and Transverse;

8. Optical Fibre works on the principle of

a) Total internal reflections

b) Refraction

c) Scattering

d) Interference

Answer. a) Total internal reflections;

Optical fibers work on the principle of total internal reflection. Total internal reflection occurs when light traveling within a denser medium (such as glass or plastic) strikes the boundary with a less dense medium (typically air) at an angle greater than the critical angle. Instead of passing through the boundary, the light reflects entirely back into the denser medium.

In optical fibers, a core made of a highly transparent material (usually glass or plastic) is surrounded by a cladding layer with a lower refractive index. When light enters the core at an angle greater than the critical angle, it undergoes total internal reflection, effectively bouncing back and forth within the core. This allows light signals to be transmitted through the fiber with minimal loss over long distances.

Optical fibers are used extensively in telecommunications, internet data transmission, and various optical applications due to their ability to transmit data at high speeds over long distances with low signal loss, thanks to the principle of total internal reflection.

9. Which one of the following phenomena is used in optical fibers?

a) Interference

b) Refraction

c) Total internal reflection

d) Polarisation

Answer. c) Total internal reflection

10. Consider the following statements-

1. Fibre optics is based on the principle of total internal reflection.

2. In an optical fiber communication system, power consumption is extremely low.

3. Optical fiber communications are free from radio frequency interference.

4. In India, Reliance Group of Industries engages in the manufacture of optical fiber.

Which of the statements is correct-

a) 1,2, and 3

b) 1,2 and 4

c) 1,3, and 4

d) 2,3, and 4

Answer. a) 1,2, and 3

11. The reason of Mirage is

a) Interference of light

b) Diffraction of light

c) Polarization of light

d) Total internal reflection of light

Answer. d) Total internal reflection of light;

The phenomenon of a mirage is primarily caused by the refraction (bending) of light as it passes through air layers with different temperatures and densities. Mirages often occur in hot desert environments, but they can also be observed on hot roads or surfaces.

So, a mirage is essentially an optical illusion caused by the bending of light due to temperature differences in the air near the ground. It can create the appearance of water or objects that aren't really there, which can be misleading in arid or hot environments.

12. A shredded diamond shines with twinkling-

a) Due to total internal reflection

b) Due to light absorption

c) Due to some natural qualities

d) Due to its molecular structure

Answer. a) Due to total internal reflection;

A shredded diamond would not shine or twinkle in the same way as an intact diamond. The optical properties of a diamond, including its brilliance and sparkle, are a result of its highly reflective and refractive qualities. These properties are dependent on the diamond's well-cut facets and polished surface.

13. Which of the following is used to take 3-dimensional pictures.

a) Photography

b) Holography

c) Radiography

d) None of the above

Answer. b) Holography;

Photography: Photography is the process of capturing images using a camera or other light-sensitive devices. It involves exposing a photosensitive material, traditionally film or a digital sensor, to light. When light strikes the photosensitive surface, it creates a chemical or digital representation of the scene being photographed. Photography has a wide range of applications, from artistic and creative photography to scientific and documentary purposes.

Holography: Holography is a technique that captures three-dimensional information about objects and displays it as a hologram. Unlike traditional photographs, holograms record both the amplitude and phase of light waves, allowing for the recreation of a 3D image that appears to have depth and parallax. Holography is used in security applications (like holographic seals on credit cards), art, and scientific visualization.

14. Television signals can't be received beyond a certain distance because-

a) Signals are weak

b) Antenna is weak

c) Air absorbs signals

d) The surface of the earth is curved

Answer. d) The surface of the earth is curved;

Television signals can't be received beyond a certain distance primarily due to the limitations of the Earth's curvature and the characteristics of electromagnetic waves. 

15. The technique used to transmit audio signals in television broadcasts is -

a) Amplitude Modulation

b) Frequency Modulation

c) Pulse code modulation

d) Time division Multiplexing

Answer. b) Frequency Modulation;

The technique used to transmit audio signals in television broadcasts is known as Frequency Modulation (FM). FM is a modulation method that encodes information, such as audio, onto a carrier wave by varying the frequency of the carrier wave in accordance with the audio signal. In television broadcasts, both video and audio signals are transmitted simultaneously.

15. The image formed on the Retina is -

a) Equal to object but inverted

b) Smaller than an object but straight

c) Smaller than an object but inverted

d) Equal to object but straight

Answer. c) Smaller than an object but inverted;

The image formed on the retina is an inverted (upside-down) and reversed (left-right) representation of the external visual scene. This inversion and reversal occur due to the way light rays from objects pass through the lens of the eye and are focused onto the retina.

16. The blue color of the ocean is due to -

a) Scattering of light

b) Dispersion of light

c) Light interference

d) The sun emits more light than other colors.

Answer. a) Scattering of light due to scattering of light from water particles.

The blue color of the ocean is primarily due to a phenomenon called Rayleigh scattering.

17.  Bats can fly during dark nights and also prey. This is because

a) The pupil of their eyes is large

b) Their night vision is very good

c) Every bird can do this

d) They produce ultrasonic waves and are guided by them

Answer. d) They produce ultrasonic waves and are guided by them;

Bats can fly during dark nights and prey successfully primarily because of their highly developed echolocation abilities. Echolocation is a biological sonar system that bats and some other animals use to navigate, locate objects, and hunt in complete darkness.

18. A decibel unit is used to measure the 

a) In measuring the intense of light

b) To measure the intensity of sound

c) To measure the magnitude of the earthquake

d) None of the above

Answer. b) To measure the intensity of sound;

Decibels are commonly used to measure the intensity or loudness of sound. It quantifies how much louder or quieter a sound is compared to a reference level. For example, sound pressure level (SPL) in decibels is used to express how loud a sound is relative to a standard reference sound pressure level.

19. As per the WHO, the safe noise level for a city is

a) 45 db

b) 50 db

c) 55 db

d) 60 db

Answer. c) 55 db;

The World Health Organization (WHO) recommends specific noise level guidelines for various environments, including urban areas. According to WHO guidelines, the safe noise level for an urban area during the daytime is 55 decibels (dB) or lower.

20. Sound above what level is considered hazardous noise pollution?

a) 30 db

b) 100 db

c) 80 db

d) 120 db

Answer. c) 80 db;

Sound levels above 70 decibels (dB) are generally considered hazardous noise pollution, especially when sustained over time or occurring frequently. Prolonged exposure to noise levels at or above this threshold can have adverse effects on human health, including Hearing Damage.

21. What type of legitimate magnetic radiation is used under the remote control of a television receiver?

a) Visible 

b) Ultraviolet

c) Infrared

d) None of the above

Answer. c) Infrared;

Visible Light:

Visible light encompasses the colors of light that are visible to the human eye, typically spanning wavelengths from approximately 400 to 700 nanometers (nm).

Applications of visible light include everyday vision, photography, art, and colorimetry for measuring and specifying colors.

Ultraviolet (UV) Light:

UV light consists of electromagnetic waves with shorter wavelengths than visible light, typically ranging from about 10 nm to 400 nm.

Uses of UV light include:

Sterilization: UV-C light is used for disinfection and sterilization purposes, such as in water treatment, air purification, and surface sanitation.

Forensics: UV light can reveal hidden evidence at crime scenes by making certain substances (like bodily fluids or fluorescent materials) fluoresce.

Sunscreen: UV-absorbing compounds are used in sunscreens to protect the skin from harmful UV radiation.

Insect Attraction: Some bug zappers and insect traps use UV light to attract and capture insects.

Astronomy: UV telescopes and observatories help astronomers study celestial objects and phenomena not visible in the visible spectrum.

Infrared (IR) Light:

IR light consists of longer wavelengths than visible light, typically ranging from about 700 nm to 1 millimeter (mm).

Applications of IR light include:

Thermography: Infrared cameras can capture thermal images, allowing for temperature measurements and heat source detection. It's used in industries like building inspection and medicine.

Night Vision: Infrared night vision technology enables enhanced visibility in low-light or complete darkness, often used in military and surveillance applications.

Remote Sensing: Infrared imaging is employed in remote sensing to study Earth's surface temperature, vegetation health, and more.

Communication: IR is used in some forms of wireless communication, such as TV remote controls.

Astronomy: Infrared telescopes help astronomers observe celestial objects that emit IR radiation, such as distant stars and galaxies.

22. Which of the following radiation types has the most energy?

a) Invisible rays

b) X-ray

c) Ultraviolet

d) Infrared

Answer. b) X-ray

23. Which of the following electrical radiations has maximum energy?

a) Visible light

b) Infrared rays

c) Ultraviolet

d) X-Rays

Answer. d) X-Rays;

Gamma rays: 

Gamma rays have extremely high energy, typically ranging from hundreds of kiloelectronvolts (keV) to several megaelectronvolts (MeV). They have frequencies in the exahertz (EHz) or higher range, which is beyond the visible and ultraviolet regions of the electromagnetic spectrum.

Gamma rays have extremely short wavelengths, often less than 0.01 nanometers (nm).


Energy: X-rays have a wide range of energy levels, from a few electronvolts (eV) to several megaelectronvolts (MeV), depending on their use.

Frequency: X-rays typically have frequencies in the petahertz (PHz) to exahertz (EHz) range.

Wavelength: X-ray wavelengths vary but generally fall in the range of 0.01 nm to several nanometers.

Ultrasound (Sound Waves):

Energy: The energy of ultrasound waves is relatively low compared to electromagnetic waves. It's typically expressed in terms of acoustic pressure or intensity.

Frequency: Ultrasound waves have frequencies in the kilohertz (kHz) to megahertz (MHz) range, depending on the application.

Wavelength: Ultrasound wavelengths vary with frequency but are typically in the millimeter to micrometer range.

Infrared Radiation (IR):

Energy: Infrared radiation has lower energy compared to visible light but higher than microwave and radio waves. The energy is expressed in electronvolts (eV).

Frequency: Infrared radiation spans the terahertz (THz) to gigahertz (GHz) range.

Wavelength: Infrared wavelengths typically range from about 1 micron (μm) to 1 millimeter (mm).

24. A laser is a device for producing

a) Spontaneous radiation

b) Dispersed radiation 

c) Scattered Radiation

d) Stimulated radiation

Answer. d) Stimulated radiation;

A laser is a device for producing highly focused and coherent light, typically in the form of a narrow, intense beam of light. The term "laser" stands for "Light Amplification by Stimulated Emission of Radiation."

Spontaneous Radiation:

Spontaneous radiation refers to the emission of electromagnetic radiation (usually photons) by an atom or molecule without any external stimulation or influence. It occurs when an electron in an excited energy state naturally transitions to a lower energy state, releasing energy in the form of a photon. 

Dispersed Radiation: 

Dispersed radiation typically refers to electromagnetic radiation (light) that has been separated into its constituent wavelengths or colors, often using a prism or diffraction grating. Dispersed radiation allows for the analysis of the spectrum of light, revealing the specific wavelengths or frequencies present in the radiation.

Scattered Radiation: 

Scattered radiation refers to the redirection of electromagnetic radiation in various directions when it interacts with matter. There are two primary types of scattered radiation:

Rayleigh Scattering: 

This occurs when radiation interacts with small particles or molecules that are much smaller than the wavelength of the radiation. Rayleigh scattering is responsible for the blue color of the sky.

Compton Scattering: 

Compton scattering occurs when X-rays or gamma rays interact with electrons, resulting in the scattering of higher-energy X-rays at different angles. It is important in medical imaging and the study of high-energy radiation.

Stimulated Radiation: 

Stimulated radiation, also known as stimulated emission, is a fundamental process that occurs in lasers. It is the opposite of spontaneous radiation. In stimulated emission, an incoming photon stimulates an excited atom or molecule to release an additional photon of the same energy, direction, and phase. This process leads to the amplification of light, creating a coherent and highly directional laser beam.

25. Bacteria can be seen by

a) Naked eye

b) Compound microscope

c) Hand lens

d) Electron microscope

Answer. b) Compound microscope;

Compound Microscope:

A compound microscope uses a system of multiple lenses to magnify small objects or specimens. It consists of an objective lens (near the specimen) and an eyepiece or ocular lens (where the user looks).

Compound microscopes are commonly used in biology, medicine, and materials science for observing cells, microorganisms, tissues, and small objects. They can typically achieve magnifications ranging from 40x to 1000x.

Hand Lens (Magnifying Glass):

A hand lens, also known as a magnifying glass or simple magnifier, consists of a single convex lens that produces an enlarged virtual image of an object when held close to it.

Hand lenses are portable and used for tasks that require magnification on the go. They are commonly used for reading fine print, examining small objects, and for basic field observations in fields like botany, geology, and entomology.

Electron Microscope:

Electron microscopes use a beam of electrons instead of visible light to illuminate specimens. They achieve much higher magnifications and resolution than optical microscopes. There are two main types: transmission electron microscopes (TEM) and scanning electron microscopes (SEM).

Electron microscopes are used in various scientific and industrial fields to study extremely small structures. TEM is used for examining internal structures of specimens, such as cells and nanomaterials, while SEM provides detailed 3D surface imaging. These microscopes are essential tools in fields like materials science, nanotechnology, and biology for studying submicroscopic structures.

26. The speed of light will be minimal while passing through

a) Water

b) Vacuum

c) Air

d) Glass

Answer. d) Glass

27. Consider the following statements

Assertion A During sleep, bright light is undesirable

Reason R: In bright light, the production of melatonin in the body is considerably increased

Select your answer using the codes given below:

a) (A) and (R) are both correct, and (R) is the correct explanation of (A)

a) (A) and (R) are both correct, and (R) is not the correct explanation of (A)

c) (A) is true, but (R) is false

d) (A) is false, but (R) is true

Answer. c) (A) is true, but (R) is false

28. Which light is most effective in photosynthesis?

a) Red

b) Blue

c) Green

d) Violet

Answer. a) Red;

Chlorophyll, the pigment responsible for photosynthesis in plants and other photosynthetic organisms, primarily absorbs light in two regions of the electromagnetic spectrum:

Blue Light: Chlorophyll absorbs blue light most effectively in the range of approximately 430 to 450 nanometers (nm) and 640 to 680 nm. This is why plants often appear green to our eyes since they reflect green light (around 500 to 570 nm) rather than absorbing it. Blue light plays a significant role in driving photosynthesis by energizing electrons within chlorophyll molecules.

Red Light: Chlorophyll also absorbs red light efficiently, particularly in the range of about 640 to 680 nm. Red light, along with blue light, is essential for photosynthesis and contributes to the overall energy needed to convert carbon dioxide and water into glucose and oxygen.

While blue and red light are the most effective in driving photosynthesis, other wavelengths of light, including violet and orange, also play a role in the process, though to a lesser extent. This is why many artificial grow lights used in horticulture and indoor farming often emphasize blue and red wavelengths to optimize plant growth and photosynthesis.

29. The sky appears blue due to 

a) Diffraction of light

b) Reflection of light

c) Refraction of light

d) Scattering of light

Answer.  d) Scattering of light;

The sky appears blue primarily due to a phenomenon called Rayleigh scattering. As sunlight enters the atmosphere, it encounters gas molecules and tiny particles, such as dust and water droplets. These particles scatter sunlight in all directions, and this scattering is more efficient for shorter wavelengths of light, such as blue and violet.

30. The sun appears red during sunset

a) Reflection of light

b) Scattering of light

c) Refraction of light

d) Diffraction of light

Answer. b) Scattering of light;

The sun appears red during sunset (and sunrise) primarily due to a phenomenon known as atmospheric scattering. 

31. The red color of the sun at sunset and sunrise is due to

a) Scattering of light

b) Refraction of light

c) Total internal reflection of light

d) Dispersion of light

Answer. a) Scattering of light

32.  An Astronaut sees the color of the sky as

a) Blue

b) White

c) Black

d) Red

Answer. c) Black;

An astronaut in space, beyond Earth's atmosphere, would not see a blue sky like we do on Earth. Instead, the sky would appear completely black. This is because there is no atmosphere in space to scatter sunlight and create the blue appearance we see on our planet.

33. When we see the sky from a plane at high altitude, then it seems-

a) Blue

b) Black

c) White

d) Red

Answer. b) Black

34. The ( Green) Grass appears green to us because

a) It reflects green color light to our eyes

b) It absorbs green color light

c) It reflects all other color lights except that of green color

d) None of the above

Answer. a) It reflects green color light to our eyes;

The green color appears green to us primarily because of the way our eyes and brain perceive and interpret the wavelengths of light that are reflected or emitted by objects.

we perceive an object as green when it reflects or emits light primarily in the green part of the spectrum, and our eyes and brain are sensitive to and capable of detecting that specific wavelength range.

35. The concept of an expanding universe is based on -

a) Doppler effect

b) Stark effect

c) Zeeman effect

d) Raman effect

Answer. a) Doppler effect;

Doppler Effect:

The Doppler Effect is a change in the observed frequency or wavelength of a wave (usually associated with sound or light) in relation to an observer moving relative to the source of the wave.

It occurs when a source of waves (e.g., sound waves or light waves) is in motion relative to an observer. If the source is moving toward the observer, the waves are compressed, resulting in a higher frequency (blue shift). If the source is moving away from the observer, the waves are stretched, resulting in a lower frequency (red shift).

The Doppler Effect has various applications, such as in radar technology, astronomy (to determine the motion of celestial objects), and medical imaging (e.g., Doppler ultrasound for measuring blood flow).

Stark Effect:

The Stark Effect is the shifting and splitting of spectral lines (emission or absorption lines) in the presence of an electric field. It occurs when charged particles, such as electrons in atoms or ions, interact with an external electric field.

The Stark Effect leads to changes in the energy levels of electrons in the presence of the field, causing shifts in the wavelengths of emitted or absorbed light.

It has applications in atomic and molecular spectroscopy, allowing scientists to study the electric fields within atoms and molecules.

Zeeman Effect:

The Zeeman Effect is the splitting of spectral lines in the presence of a magnetic field. It occurs when atoms or ions with magnetic moments (associated with the intrinsic spin and orbital angular momentum of electrons) interact with an external magnetic field.

The Zeeman Effect results in the splitting of spectral lines into multiple components, revealing information about the magnetic properties of the atomic or molecular species.

It is used in various scientific fields, including astrophysics, to study the magnetic fields of stars and planets.

Raman Effect:

The Raman Effect is a phenomenon in which the scattering of light by molecules or crystals results in a shift in the frequency of the scattered light. This shift is due to the interaction between incident photons and vibrational or rotational modes of the scattering material.

The Raman Effect provides valuable information about the vibrational and rotational energies of molecules, making it a powerful tool for chemical analysis and materials characterization.

It has applications in chemistry, spectroscopy, and materials science.

36. In driving a car which type of mirror would you like to use for observing traffic at your back?

a) Concave mirror

b) Spherical Mirror

c) Convex mirror

d) Plain Mirror

Answer. c) Convex mirror;

Concave Mirror:

Concave mirrors are curved inward, with a reflecting surface that curves inward like the inside of a sphere.

Concave mirrors can focus light to a point, making them useful in devices like makeup mirrors, shaving mirrors, and some types of telescopes (e.g., Newtonian telescopes).

They are also used in certain optical instruments, such as magnifying glasses, dental mirrors, and headlights in automobiles, to produce real or virtual images, depending on the object's position relative to the mirror.

Spherical Mirror:

Spherical mirrors can refer to both concave and convex mirrors since they share the same basic spherical shape. Concave mirrors curve inward, while convex mirrors curve outward.

Spherical mirrors are used in various types of telescopes, including reflector telescopes (e.g., Newtonian telescopes) that use concave mirrors to collect and focus light.

Convex spherical mirrors are commonly used as traffic or safety mirrors to provide a wide field of view in locations like parking lots and road intersections.

Convex Mirror:

Convex mirrors are curved outward, with a reflecting surface that bulges outward.

Convex mirrors are often used in vehicles as side-view or rear-view mirrors. They provide a wider field of view, helping drivers see objects and vehicles in their blind spots.

Convex mirrors are used in stores, warehouses, and public areas for security and surveillance purposes to observe a larger area.

Plane Mirror:

Plane mirrors have a flat, non-curved reflecting surface.

Plane mirrors are the type of mirrors you encounter in everyday life, such as bathroom mirrors, dressing mirrors, and household mirrors.

They produce virtual and upright images that are the same size as the object being reflected. They do not focus or magnify light redshift.

38. Which of the following types of mirrors are used to view the traffic behind a car?

a) Convex mirror

b) Concave mirror

c) Plane mirror

d) Spherical mirror

Answer. a) Convex mirror;

Convex mirrors are used as rearview mirrors in vehicles. Convex mirrors have a curved outward shape, which causes them to diverge light rays and provide a wider field of view compared to flat or concave mirrors. It allows for a better overall view of the road, enhancing safety while driving. Convex rearview mirrors are a common feature in cars, trucks, and other vehicles for this reason.

39. Which mirror is used as a rearview mirror in vehicles?

a) Plain

b) Convex

c) Concave

d) Cylindrical

Answer. b) Convex

40. In order to avoid sunlight, which of the following color combinations for an Umbrella is most appropriate?

a) Top black and bottom white

b) Top white and bottom black

c) Only black

d) Only white

Answer. b) Top white and bottom black

41. The image formed by the astronomical telescope is

a) Virtual and diminished

b) Virtual and magnified

c) Real and diminished

d) Real and magnified

Answer. b) Virtual, inverted, and magnified;

In astronomical telescopes, the primary goal is to gather and magnify light from distant celestial objects, making them appear larger and brighter. The inverted nature of the intermediate image formed by the objective is not an issue because the orientation of celestial objects in the night sky does not matter for astronomical observations. Astronomers are primarily concerned with studying the details, positions, and properties of celestial objects, rather than their visual orientation.

42. The number of images of an object placed between two parallel is -

a) Two

b) One

c) Six

d) Infinite

Answer. d) Infinite;

When an object is placed between two parallel mirrors, the number of images formed can be infinite. This is a result of multiple reflections between the two mirrors.

The number of images increases with each additional reflection. While theoretically, the number of images is infinite, in practice, they become fainter and less distinguishable as the number of reflections increases. The intensity of each successive image is typically reduced due to losses from absorption and reflection in the mirrors.

So, while there can be an infinite number of images in theory, in practice, only a few are typically observed and considered significant due to their diminishing brightness.

43. How many images will be formed if a point light source is placed between parallel plane mirrors?

a) Two

b) four

c) Eight

d) Infinite

Answer. d) Infinite

44. Which one of the following colors is seen in the middle of the rainbow?

a) Blue

b) Green

c) Red

d) Yellow

Answer. b) Green;

In the middle of a rainbow, you typically see the color green. Rainbows are composed of a spectrum of colors that include red, orange, yellow, green, blue, indigo, and violet. These colors are arranged in a circular arc with red on the outer edge and violet on the inner edge.

The specific sequence of colors in a rainbow is often remembered using the acronym "ROYGBIV," which stands for Red, Orange, Yellow, Green, Blue, Indigo, and Violet. When sunlight is refracted (bent) and internally reflected within raindrops, it separates into various colors, creating the beautiful and colorful phenomenon we know as a rainbow. Green is situated in the middle of this sequence of colors, which is why it's the color most commonly seen at the center of a rainbow.

45. An air bubble in water will act like a

a) Convex mirror

b) Convex lens

c) Concave mirror

d) Concave lens

Answer. d) Concave lens;

Convex Mirror:

A convex mirror has an outward-curved surface, which causes light to diverge (spread out) upon reflection.

Convex mirrors are commonly used as side-view and rearview mirrors in vehicles. They provide a wider field of view, reducing blind spots.

They are also used in stores, parking lots, and other public areas for security and surveillance to observe a larger area.

Convex Lens:

A convex lens is thicker at the center and thinner at the edges, causing light to converge (focus) when it passes through.

Convex lenses are used in magnifying glasses, cameras, and binoculars to produce enlarged and upright images of distant objects.

Convex lenses can be used to correct hyperopia (farsightedness) in eyeglasses, as they bring distant objects into focus.

Concave Mirror:

A concave mirror has an inward-curved surface, causing light to converge upon reflection.

Concave mirrors are often used in reflecting telescopes (e.g., Newtonian telescopes) to collect and focus light for astronomical observations.

Some makeup mirrors use concave mirrors to produce magnified images.

Concave Lens:

A concave lens is thinner at the center and thicker at the edges, causing light to diverge (spread out) when passing through.

Concave lenses are used to correct myopia (nearsightedness) in eyeglasses, as they help bring close objects into focus.

They are used in optical systems, such as microscopes and projectors, to produce virtual and diminished images of objects.

46. An air bubble inside water behaves as 

a) Bifocal lens

b) Convergent Lens

c) Divergent lens

d) Cylindrical lens

Answer. c) Divergent lens;

Bifocal Lens:

Bifocal lenses are eyeglass lenses designed to correct both nearsightedness (myopia) and farsightedness (hyperopia) in a single lens.

Bifocal lenses have two distinct regions with different optical powers. The upper part of the lens corrects distance vision, while the lower part (usually in a "D" or "segment" shape) corrects near vision.

Bifocal lenses are commonly used by individuals who need both distance and near vision correction, such as for reading or other close-up tasks.

Convergent Lens (Convex Lens):

Convergent lenses are thicker at the center than at the edges, and they converge (focus) parallel rays of light.

Convergent lenses are used in various optical applications, including eyeglasses for farsightedness, magnifying glasses, cameras, and telescopes, to produce focused and magnified images of distant objects.

Divergent Lens (Concave Lens):

Divergent lenses are thinner at the center and cause parallel rays of light to diverge (spread out).

Divergent lenses are used to correct nearsightedness (myopia) in eyeglasses. They help spread out incoming light to bring close objects into focus on the retina.

Cylindrical Lens:

Cylindrical lenses have different curvatures in different meridians. They are used to correct astigmatism, an optical condition where the cornea or lens has an irregular shape, causing blurred or distorted vision.

Cylindrical lenses have a prescription that includes both spherical (for nearsightedness or farsightedness) and cylindrical (for astigmatism) components.

Cylindrical lenses are essential for individuals with astigmatism to correct the uneven curvature of the eye's optical elements.

47. The height of a plane mirror to see the full-size image of a person is equal to

a) The height of the person

b) Half of the height of the person

c) One-fourth the height of the person

d) Double the height of the person

Answer. b) Half of the height of the person;

To see a full-size image of a person in a plane mirror, the mirror should be positioned so that the person's eyes are at the same height as the mirror's center. In other words, the height of the mirror should be roughly half the height of the person. This ensures that the person's eyes, head, and body are all reflected in the mirror, giving the appearance of a full-size image.

48. The minimum height of the mirror required to see the whole stand-up image of a man of height 1.50 meters shall be

a) 0.75 metre

b) 1.00 metre

c) 1.50 metre

d) 3.00 metre

Answer. a) 0.75 metre

49. Which one of the following statements is not true for a person suffering from hypermetropia?

a) The person can see objects distinctly

b) The focal length of the lens is large

c) The image of the close objects focussed behind the retina

d) A concave lens is used to correct this defect.

Answer. d) A concave lens is used to correct this defect.

Hypermetropia, also known as farsightedness or hyperopia, is a common vision condition where distant objects are seen more clearly than nearby objects. This occurs because light entering the eye focuses behind the retina rather than directly on it. 

Hypermetropia can be caused by an eyeball that is too short or a cornea with too little curvature. These factors prevent incoming light from converging properly onto the retina.

 Hypermetropia can be corrected with the use of eyeglasses or contact lenses that have a converging (convex) lens. These lenses help focus incoming light onto the retina, allowing for clearer vision at all distances.

50. Which of the following lenses is used to correct myopia?

a) Convex lens

b) Concave lens

c) Cylindrical lens

d) None of these

Answer. b) Concave lens;

Concave lenses, also known as divergent lenses, are used to correct myopia, which is commonly referred to as nearsightedness. Myopia occurs when the eye's optical system focuses incoming light in front of the retina, making distant objects appear blurry. Concave lenses help to correct this by spreading out incoming light rays, which allows them to converge properly on the retina.

51. A myopic eye can be corrected by using a

a) Convex lens

b) Concave lens

c) Cylindrical lens

d) Plane convex lens

Answer. b) Concave lens;

Myopic (nearsighted) eyes can be corrected using concave lenses, also known as divergent lenses. These lenses are designed to correct the vision of individuals with myopia, where distant objects appear blurry because light entering the eye focuses in front of the retina instead of directly on it.

Concave lenses are characterized by their thinner centers and thicker edges. They cause incoming light rays to spread out (diverge) before entering the eye. This divergence of light compensates for the excessive focusing power of the myopic eye, allowing the light to properly focus on the retina. As a result, the corrected myopic eye can see distant objects more clearly.

52. For the myopic eye, the defect is cured by

a) Convex lens

b) Concave lens

c) Cylindrical lens

d) None of the above

Answer. b) Concave lens

53. The focusing in the eye is done by -

a) Change in the convexity of the lens

b) To and from the movement of the lens

c) To and from the movement of the retina

d) Change in the refractive index of the eye fluid

Answer. a) Change in the convexity of the lens

54. Which one of the following statements is not correct?

a) Mirage is an optical illusion arising due to the total internal reflection of light

b) Concave mirrors are used in searchlights.

c) In summer, white or light-colored clothes are preferred to dark-colored clothes generally

d) A convex mirror with a small aperture is used by doctors to examine the ears, nose, or throat of patients.

Answer. d) A convex mirror with a small aperture is used by doctors to examine the ears, nose, or throat of patients.

55. In Mirror, which is used in searchlights is-

a) Concave mirror

b) Convex mirror

c) Simple mirror

d) None of these

Answer. a) Concave mirror

56. The least distance of distinct vision is ( cm)

a) 25

b) 5

c) 75

d) 100

Answer. a) 25;

The least distance of distinct vision, also known as the near point, is the closest distance at which the human eye can focus on an object clearly without straining. This distance varies from person to person but is typically considered to be around 25 centimeters (approximately 10 inches) for a person with normal vision. Beyond this distance, the eye needs to accommodate (adjust its focus) to see objects clearly.

57. The minimum distance of clear vision for a normal healthy eye of the human being is supposed to be 

a) 50 cm

b) 10 cm

c) 15 cm

d) 25 cm

Answer. d) 25 cm

58. Power of the Sunglass is

a) 0 dioptre

b) 1 dioptre

c) 2 dioptre

d) 4 dioptre

Answer. a) 0 dioptre;

Sunglasses are eyewear designed to protect the eyes from bright sunlight and harmful ultraviolet (UV) radiation. They serve both functional and aesthetic purposes

59. Retina of the eye is comparable to which of the following parts of a traditional Camera?

a) Film

b) Lens

c) Shutter

d) Cover

Answer. a) Film;

The retina of the Eye:

The retina is the light-sensitive tissue located at the back of the eye.

It contains millions of specialized photoreceptor cells, such as rods and cones, that capture incoming light and convert it into electrical signals.

These electrical signals are then transmitted to the brain through the optic nerve, where they are processed to form visual images.

Image Sensor of a Camera:

The image sensor in a traditional camera serves a similar function to the retina in the eye.

It is a light-sensitive component that captures incoming light when you take a photograph.

The image sensor consists of individual pixels (photosites) that convert light into electrical signals.

These electrical signals are processed and stored as a digital image file.

60. The number of colors contained in the sunlight is 

a) 3

b) 5

c) 6

d) 7

Answer. d) 7

61. Long radio waves are reflected by which of the following layers of Earth's surface-

a) Troposphere

b) Ionosphere

c) Troposphere

d) Stratosphere

Answer. b) Ionosphere;

The ionosphere is a region of Earth's upper atmosphere that contains a high concentration of ions and free electrons. It extends from approximately 30 miles (48 kilometers) above the Earth's surface to about 600 miles (965 kilometers) or more into space. 

The ionosphere is named for its high ionization level. Solar radiation from the sun, particularly in the form of ultraviolet (UV) and X-ray radiation, is responsible for ionizing the gases in this region, primarily oxygen and nitrogen. This ionization process results in the creation of positively charged ions and free electrons.

62. Wireless communication is reflected back to the earth's surface by the 

a) Troposphere

b) Stratosphere

c) Ionosphere

d) Exosphere

Answer. c) Ionosphere

63. Which one of the following statements is not true about cosmic rays?

a) They are electromagnetic waves

b) They have a very short wavelength

c) They are made of highly energetic charged particles

d) They originate from the sun

Answer. a) They are electromagnetic waves;

Cosmic Rays:

Cosmic rays are high-energy particles, primarily protons, electrons, and atomic nuclei, that originate from sources beyond our solar system. These sources can include supernovae (exploding stars), active galactic nuclei, and other astrophysical processes.

Cosmic rays are composed of atomic nuclei, which can range from hydrogen nuclei (protons) to heavier elements like iron. They also contain electrons and positrons (antiparticles of electrons).

Cosmic rays can be electrically charged (like protons and electrons) or electrically neutral (like gamma rays and neutrons).

Electromagnetic Rays (Light):

Electromagnetic rays, also known as electromagnetic radiation, encompass a wide range of energy, from very low-energy radio waves to high-energy gamma rays. They are emitted by various astronomical sources and objects, such as stars, galaxies, and black holes.

Electromagnetic rays consist of oscillating electric and magnetic fields that propagate through space as waves. The electromagnetic spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays, ordered by increasing energy and decreasing wavelength.

Electromagnetic rays are electrically neutral and do not consist of charged particles like cosmic rays.

Electromagnetic rays interact with matter differently depending on their energy. Low-energy forms, like radio waves and microwaves, can pass through many materials with minimal interaction. High-energy forms, such as X-rays and gamma rays, can ionize atoms and damage living tissue.

Electromagnetic rays are commonly detected and studied using telescopes and detectors sensitive to specific wavelengths of light. Different types of telescopes are used to capture various regions of the electromagnetic spectrum.

64. Waves used for telecommunication are

a) Visible light

b) Infrared

c) Ultraviolet

d) Microwave

Answer. d) Microwave;

Waves used for telecommunications include various forms of electromagnetic waves, primarily radio waves, microwaves, and light waves (in the form of optical fibers). These waves are used to transmit information, such as voice, data, and video, over various communication systems. 

Radio Waves:

Radio waves are a type of electromagnetic wave with relatively long wavelengths.

They are commonly used for wireless communication, including AM (Amplitude Modulation) and FM (Frequency Modulation) radio broadcasting, television broadcasting, and cellular communication.

Radio waves are also used in technologies like Wi-Fi, Bluetooth, and GPS for data transmission and location services.


Microwaves are electromagnetic waves with shorter wavelengths than radio waves but longer wavelengths than visible light.

They are used extensively in various applications, including microwave ovens, radar systems (for weather forecasting and air traffic control), satellite communication, and certain wireless technologies.

Cellular networks often rely on microwave links for backhaul, connecting cell towers to the broader network.

65. A CT Scan is done by using

a) Infrared Rays

b) Ultrasonic Waves

c) Visible light

d) X-Rays

Answer. d) X-Rays;

66. The sound will have the highest velocity in

a) Vacuum

b) Air

c) Water

d) Steel

Answer. d) Steel

67. Sound waves-

a) Can travel in a vacuum

b) Can travel only in solid

c) Can travel only in gases

d) Can travel both in solid and gaseous medium

Answer. d) Can travel both in solid and gaseous medium;

Sound waves are mechanical waves that propagate through a medium, typically through the air but also through other materials like water or solids. They carry energy from one place to another in the form of compressions and rarefactions, causing particles in the medium to vibrate.

68. In which of the following options, can sound not travel?

a) Water

b) Vacuum

c) Iron

d) Air

Answer. b) Vacuum

69. The walls of the hall, built for music concerts should-

a) Amplify sound

b) Transmit sound

c) Reflect Sound

d) Absorb sound

Answer. d) Absorb sound;

Amplify Sound:

Amplifying sound involves increasing the intensity or volume of a sound wave. This is commonly done using electronic devices like amplifiers, which take a weak audio signal as input and produce a louder output signal without significantly altering the wave's characteristics.

Amplification is essential in audio systems, including speakers and microphones, to make sounds audible to a larger audience.

Transmit Sound:

Transmitting sound refers to the process of sending sound waves through a medium, such as air or water, from one location to another. Sound can be transmitted through various means, including air, water, and solid materials.

Examples of sound transmission methods include speaking to someone over a phone, the sound of a musical instrument traveling through the air, and sound waves traveling through the Earth's crust in the form of seismic waves.

Reflect Sound:

Reflecting sound involves the redirection of sound waves off a surface. When sound waves encounter a reflective surface, they bounce off it and change direction.

Sound reflection is commonly observed when sound waves hit surfaces like walls, floors, and ceilings in a room, creating echoes and influencing the acoustics of the space.

Reflective surfaces are used intentionally in architectural design to enhance or control sound quality in concert halls, theaters, and other venues.

Absorb Sound:

Absorbing sound means reducing the intensity of sound waves by converting their energy into other forms, such as heat. Sound-absorbing materials are used to dampen or attenuate sound.

Examples of sound-absorbing materials include acoustic panels, foam, curtains, and certain textiles. These materials are often used in environments where sound reflection and reverberation need to be minimized to create quieter and more comfortable spaces, such as recording studios and offices.

70. To hear a clear echo, the minimum distance between the reflecting surface and the observer should be

a) 165 feet

b) 165 meter

c) 16.5 feet

d) 16.5 meter

Answer. d) 16.5 meter

71. An astronaut cannot hear his companion at the surface of the moon because 

a) Produced frequencies are above the audio

b) Temperature is too low during the night and too high during the day

c) There is so medium for sound propagation

d) There are many craters on the surface of the moon

Answer. c) There is so medium for sound propagation;

Astronauts on the surface of the Moon cannot hear their companions or any other sounds in the traditional sense due to the lack of a medium for sound to travel through.

72. Consider the following statements about ultrasonic waves-

1. They can destroy insects

2. They can clean clothes by removing dust

3. They can be used to treat diseases

4. They can control automatic doors.

Of the above statements-

a) 1 and 2 are correct

b) 3 and 4 are correct

c) 1,2, and 3 are correct

d) All are correct

Answer. d) All are correct;

Ultrasonic waves, also known as ultrasound, are high-frequency sound waves with frequencies greater than the upper limit of human hearing, typically above 20,000 hertz (Hz). Ultrasonic waves have a wide range of applications in various fields due to their ability to travel through solids, liquids, and gases and their interaction with matter.

Here are some common uses of ultrasonic waves:

Medical Imaging:

Ultrasonic imaging, or ultrasound, is widely used in medicine for diagnostic purposes. It allows healthcare professionals to visualize the internal structures of the body, including organs, blood vessels, and developing fetuses during pregnancy.

Nondestructive Testing (NDT):

Ultrasonic testing is a critical method in the field of nondestructive testing (NDT). It is used to inspect the integrity of materials, welds, and structures by sending ultrasonic waves into the material and analyzing the reflected waves.


Ultrasonic cleaning uses high-frequency sound waves in a liquid to create microscopic bubbles that collapse and generate tiny shock waves. These shock waves help dislodge and remove contaminants from surfaces, including delicate items like jewelry, surgical instruments, and electronics.

Distance Measurement:

Ultrasonic sensors, often referred to as ultrasonic rangefinders, use the time it takes for ultrasonic waves to bounce off an object and return to measure distances. They are commonly used in robotics, automotive parking assist systems, and industrial automation.

Pest Control:

Ultrasonic pest-repellent devices emit high-frequency sound waves that are unpleasant for certain pests, such as rodents and insects. These devices are used as a non-toxic and non-lethal method to deter pests from invading homes or commercial spaces.

Welding and Bonding:

Ultrasonic welding and ultrasonic bonding techniques use the mechanical vibrations of ultrasonic waves to join or bond materials together. These processes are commonly used in the manufacturing of plastics, textiles, and metals.

Animal Communication and Research:

Some animals, such as bats and dolphins, use ultrasonic waves for echolocation and communication. Researchers use ultrasonic detectors to study and monitor these animals.

Sonar and Underwater Navigation:

Sonar (Sound Navigation and Ranging) systems use ultrasonic waves underwater for navigation, communication, and mapping. Submarines, ships, and underwater robots utilize sonar technology for underwater exploration.

73. Ultrasonics are sound waves of frequency-

a) Greater than 20000 Hz

b) Less than 10000 Hz

c) Equal to 1000 Hz

d) None of these

Answer.  a) Greater than 20000 Hz;

The frequency of an ultrasonic wave refers to the number of complete cycles or oscillations that occur per second. Ultrasonic waves, as the name suggests, have frequencies higher than the upper limit of human hearing, which is typically considered to be 20,000 hertz (Hz). Therefore, ultrasonic waves have frequencies greater than 20,000 Hz.

74. In SONAR, we use ( UPPSC PYQ)

a) Radio waves

b) Audio Sound Waves

c) Ultrasonic Waves

d) Infrasonic Waves

Answer. c) Ultrasonic Waves;

SONAR stands for "Sound Navigation and Ranging." It is a technology that uses sound waves to detect, locate, and measure objects underwater. SONAR is similar in principle to radar (Radio Detection and Ranging) but uses sound waves instead of radio waves because sound travels efficiently through water

75. The wavelength extension of visible light is

a) Between 200-900 nm

b) Between 250-850 nm

c) Between 300-800 nm

d) Between 390-780 nm


Answer. d) Between 390-780 nm

76. The human eye is most sensitive to visible light of the wavelength.

a) 6050 A'

b) 5500 A'

c) 4500 A'

d) 7500 A'

Answer. b) 5500 A'

The human eye is most sensitive to visible light with a wavelength of approximately 555 nanometers (nm). This corresponds to the green-yellow part of the visible spectrum. This sensitivity is reflected in the eye's color perception and visual acuity.

77. Light appears to travel in a straight line because-

a) It consists of small particles

b) The velocity of light is very large

c) The wavelength of light is very small

d) Light is reflected by the surroundings

Answer. c) The wavelength of light is very small

78. Which of the following has the highest velocity?

a) Cosmic rays

b) Light

c) Electron

d) Supersonic wave

Answer. b) Light;

Cosmic Rays:

The velocities of cosmic rays can range from a fraction of the speed of light to extremely high energies approaching the speed of light. Some cosmic rays are relativistic particles, meaning they travel at a significant fraction of the speed of light, which is approximately 299,792,458 meters per second (or about 186,282 miles per second).

Light (Electromagnetic Waves):

Light, which includes all forms of electromagnetic waves, including visible light, travels at the speed of light in a vacuum, which is approximately 299,792,458 meters per second (about 186,282 miles per second). In other media, such as air or glass, light travels at slightly lower speeds, but it is still very fast.


The speed of electrons can vary depending on their energy. In everyday situations, electrons in electrical circuits typically have drift velocities on the order of millimeters per second. However, in particle accelerators and other high-energy physics experiments, electrons can be accelerated to very high velocities, approaching the speed of light.

Supersonic Waves:

The term "supersonic" refers to speeds that exceed the speed of sound in a particular medium. The speed of sound in air at room temperature is approximately 343 meters per second (about 767 miles per hour). Supersonic waves travel faster than this speed.

79. Velocity of light is maximum is 

a) Diamond

b) Water

c) Vacuum

d) Hydrogen

Answer. c) Vacuum

80. Light from the sun reaches Earth in about 

a) 2 minutes

b) 4 minutes

c) 8 minutes

d) 16 minutes

Answer. c) 8 minutes;

Light from the Sun takes approximately 8 minutes and 20 seconds to reach the Earth. This is often rounded to about 8 minutes for simplicity in everyday conversation. The exact time it takes for sunlight to travel from the Sun to the Earth is approximately 499.0 seconds. This transit time is due to the vast distance between the Sun and our planet, with the Sun located at an average distance of about 93 million miles (about 149.6 million kilometers) from Earth.

81. When light passes from one medium to another medium, which one of the following does not change-

a) Intensity

b) Velocity

c) Wavelength

d) Frequency

Answer. d) Frequency

82. Which one of the following energy conversions takes place in carrying out photosynthesis?

a) Light to chemical energy

b) Light to thermal energy

c) Thermal to biochemical energy

d) Heat to kinetic energy

Answer. a) Light to chemical energy

83. Direct viewing of the sun during a total solar eclipse causes irreversible damage to the eyes. The retinal burn is caused by one of the following components of the sun rays?

a) Heat

b) Rainbow light

c) Ultraviolet light

d) Infrared light

Answer. c) Ultraviolet light

84. The color of the star is an indication of its-

a) Distance from the earth

b) Temperature

c) Luminosity

d) Distance from the sun

Answer. b) Temperature;

The color of a star is an indication of its temperature. This is described by a principle known as Wien's Displacement Law, which states that the temperature of a star is inversely proportional to the peak wavelength of its emitted light. In simpler terms, hotter stars appear bluer or white, while cooler stars appear redder.

85. The color of light is determined by its 

a) Amplitude

b) Wavelength

c) Intensity

d) Velocity

Answer. b) Wavelength

86. The light with the shortest wavelength is 

a) Red

b) Yellow

c) Blue

d) Violet

Answer. d) Violet;

The wavelength of the color of light determines its appearance in the visible spectrum. Here are approximate wavelengths for various colors of visible light, measured in nanometers (nm):

Red light: Wavelengths range from approximately 620 nm to 750 nm.

Orange light: Wavelengths range from approximately 590 nm to 620 nm.

Yellow light: Wavelengths range from approximately 570 nm to 590 nm.

Greenlight: Wavelengths range from approximately 495 nm to 570 nm.

Blue light: Wavelengths range from approximately 450 nm to 495 nm.

Indigo light: Wavelengths range from approximately 420 nm to 450 nm (note that indigo is not always considered a distinct color in the visible spectrum).

Violet light: Wavelengths range from approximately 380 nm to 420 nm.

87. The sun and the moon appear elliptical near the horizon because of 

a) Refraction

b) Optical Illusion

c) Interference Phenomenon

d) Their actual shape

Answer. a) Refraction;

The apparent elliptical shape of the Sun and Moon, when they are near the horizon, is primarily due to an optical illusion called atmospheric refraction. Atmospheric refraction is caused by the bending of light as it passes through the Earth's atmosphere, which has varying densities at different altitudes.

88. Red light is used in traffic signals because-

a) It has the longest wavelength ( length)

b) It is beautiful

c) It is also visible to poorly lit people.

d) None of the above reasons

Answer. a) It has the longest wavelength ( length)

Red light is used in traffic signals primarily for its visibility, safety, and consistency in signaling meanings

Red light is easily distinguishable from other colors in most lighting conditions. It has a longer wavelength than many other visible colors, making it stand out well against backgrounds and in various weather conditions.

89. Assertion A- The danger signal is made up of red color.

Reason R- The red color is scattered the least.

Select the correct answer using the codes given below:

a) Both A and R are true and R is the correct explanation of A.

b) Both A and R are true but R is not the correct explanation of A

c) A is true but R is false

d) A is false but R is true

Answer. a) Both A and R are true and R is the correct explanation of A.

90. A red light signal is used as a danger signal because-

a) It is scattered least

b) This is comfortable for the eyes

c) It produces the least chemical reaction

d) It is least absorbed in air

Answer. a) It is scattered least

91. The blue color of the sky is due to - ( UPPSC PYQ 2021)

a) Scattering of light

b) Dispersion of light

c) Light interference

d) The sun emits more light than other colors.

Answer. a) Scattering of light due to dust particle 


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