Light (Physics) (Part-1)

 

Total Questions: 50

1. According to the law of reflection. [S.S.C. Online C.P.O.S.I. (T-I) 7.07.2017 (Shift-I)]

Correct Answer: (c) The angle of incidence is always equal to the angle of reflection.
Solution:

According to the law of reflection:

The angle of incidence () is equal to the angle of reflection (r).
i=r
Both the incident ray, the reflected ray, and the normal to the reflecting surface at the point of incidence lie in the same plane.

Laws of Reflection | GeeksforGeeks

2. Sun appears red at sunrise and sunset due to________. [S.S.C. Online Graduation Level (T-I) 1.09.2016 (Shift-III)]

Correct Answer: (d) that all other colours scatter away except red.
Solution:

Sun appears red at sunrise and sunset due to scattering of light — specifically, Rayleigh scattering.

Explanation:

During sunrise and sunset, sunlight passes through a larger thickness of the Earth's atmosphere.

Shorter wavelengths (blue and violet) scatter more and are removed from the direct path.
Longer wavelengths (red and orange) pass through and reach the observer’s eyes, making the Sun appear red.

3. The lens that collects the rays is called________. [S.S.C. Online Stenographer 13.09.2017 (Shift-I)]

Correct Answer: (a) Converging
Solution:A converging lens is also known as a convex lens.

It is thicker in the middle and thinner at the edges, and it causes parallel rays of light to bend inward and meet (converge) at a single point called the focus (or focal point).

Optical Lenses Convex/Concave Mirror Theory

4. Which of the following is indicated by the colour of a star? [S.S.C. Online Graduation Level (T-I) 8.09.2016 (Shift-I)]

Correct Answer: (c) temperature
Solution:

Stars emit light based on their temperature, following blackbody radiation principles.

The color you see corresponds to the peak wavelength of emitted light, which shifts with temperature.

Star ColourApprox.temperature (kelvin)Example star
Blue10,000 – 40,000 KRigel
White7,500 – 10,000 KSirius
Yellow5,000 – 6,000 KSun (approx. 5,778 K)
Orange3,500 – 5,000 KArcturus
Red2,000 – 3,500 KBetelgeuse

Based on Wien’s Displacement Law,

Hotter objects emit light at shorter wavelengths (bluer light), while cooler ones emit at longer wavelengths (redder light).

5. The instrument used to measure the intensity of light is called_______ . [S.S.C. Online CHSL (T-I) 23.01.2017 (Shift-III)]

Correct Answer: (a) Lucimeter
Solution:The intensity of light is measured by a lucimeter.

6. Which instrument is used to measure the intensity of light produced by an unknown source in terms of a standard source? [S.S.C. Online Graduation Level (T-I) 11.06.2019 (Shift-II)]

Correct Answer: (c) Photometer
Solution:An instrument used to measure the intensity of light produced by an unknown source with respect to a standard source is called a photometer.
  • The photometer makes an accurate comparison of the intensity of light received from different sources.

7. Which of the following processes is responsible for the glittering of air bubbles rising through water? [S.S.C. Online Graduation Level (T-I) 1.09.2016 (Shift-II)]

Correct Answer: (c) Total internal reflection of light
Solution:

The glittering of air bubbles rising through water is caused by the process of total internal reflection.

Explanation:

Light entering the air bubble from water undergoes multiple internal reflections inside the bubble, making it sparkle or glitter as it rises.

8. The phenomenon of change in the direction of light when it passes from one medium to another is called_______. [S.S.C. Online Graduation Level (T-I) 10.09.2016 (Shift-I)]

Correct Answer: (c) Refraction
Solution:Refraction is the bending of light as it travels from one medium to another with a different optical density (like air to water or glass).

Light changes speed when it enters a different medium:

From air to water/glass → light slows down → bends toward the normal.
From water/glass to air → light speeds up → bends away from the normal.

Examples

A pencil appears bent in a glass of water.
Lenses in glasses or cameras focus light via refraction.
Rainbows form due to refraction in raindrops.

9. Light travels fastest in _________. [S.S.C. Online CHSL (T-I) 16.01.2017 (Shift-II)]

Correct Answer: (d) Vacuum
Solution:The speed of light in a vacuum is 3.00×10⁸ m/s.
MediumSpeed of Light (m/s)
Water2.25×10⁸  
Glass2.00×10⁸ 
Oil2.04×10⁸ 
Nylon1.96×10⁸ 

Light slows down when it enters a medium denser than a vacuum (or air). The denser the medium, the slower light travels.

10. Which among the following has its refractive index closest to that of crown glass? [S.S.C. Online Graduation Level (T-I) 7.03.2020 (Shift-I)]

Correct Answer: (b) Canada balsam
Solution:Canada balsam, also known as Canada turpentine, is made from a resin obtained from the fir tree.

It is a transparent material with a refractive index (1.53) almost equal to that of crown glass.