Engineering Physics Questions and Answers – Light

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Light”.

1. How is light emitted?
a) Klystron valves
b) Radioactive decay of the nucleus
c) Transmission of high energy electrons from an excited state to a lower state
d) Acceleration of electrons
View Answer

Answer: c
Explanation: An electron is always stable in the ground state. When in an excited state, it tends to jump to a lower state. In this process, it releases a photon of energy equal to the energy difference. When the frequency of these photons lies in the visible region, we get light.

2. Who gave the quantum theory of light?
a) Albert Einstein
b) Heisenberg
c) Michaelson Morley
d) Max Planck
View Answer

Answer: d
Explanation: Max Planck proposed the quantum theory of light which states that the light consists of small particles in the form of discrete bundles of energy called photons.

3. Huygen’s wave theory of light considered light to be ____________
a) Made up of particles
b) Longitudinal Waves
c) Transverse Waves
d) Of dual nature
View Answer

Answer: b
Explanation: Huygen’s Wave Theory of Light considered Light to be a periodic disturbance that is transmitted through a medium in the form of longitudinal waves. This theory explained reflection, refraction, diffraction, and interference.


4. Michaelson-Morley experiment ruled out the existence of __________
a) Luminiferous Ether
b) Wave nature of light
c) Particle nature of light
d) Corpuscles
View Answer

Answer: a
Explanation: Earlier it was believed, that space is filled up of a medium called Ether. It was believed, that light has different speed in different directions. However, by the Michaelson-Morley experiment, it was shown that the light has the same speed in all the directions and that ether does not exist.

5. Which theory was first to consider that light requires no medium for its propagation?
a) Huygen’s Wave Theory of Light
b) Maxwell’s Electromagnetic Theory
c) Quantum theory of light
d) Corpuscular theory
View Answer

Answer: b
Explanation: In 1873, Maxwell introduced the Electromagnetic Theory which assumed the light to be an electromagnetic wave, thus it requires no medium for its propagation. It discarded the presence of ether.

6. What is the frequency of a photon having energy 2.1 X 10-30 J?
a) 3.1 X 1013 Hz
b) 4.1 X 1013 Hz
c) 5.1 X 1013 Hz
d) 6.1 X 1013 Hz
View Answer

Answer: b
Explanation: Here, E = 2.1 X 10-30 J
Frequency, v = ?
We know, Energy = hv, where h is the Planck’s Constant
Therefore, v = E/h
= 2.1 X 10-30 J/6.6 X 10-34 Js
= 3.1 X 1013 Hz.

7. The wavelength of a photon is 5000 Å. The energy of the photon is ___
a) 3.47 eV
b) 2.41 eV
c) 6.78 eV
d) 2.12 eV
View Answer

Answer: b
Explanation: We know, E = hc/λ
= 6.6 X 10-34 X 3 X 108/5 X 10-7
= 3.86 X 10-19 J
= 2.41 eV.

8. An electron makes a transition from n = 7 state to n = 3 state in the hydrogen atom. What is the frequency of the emitted photon?
a) 2 X 1014 Hz
b) 3 X 1014 Hz
c) 4 X 1014 Hz
d) 5 X 1014 Hz
View Answer

Answer: b
Explanation: The electron makes a transition from n = 7 to n = 3.
= 19.77 X 10-20J
Frequency, v = ΔE/h
= 3 X 1014 Hz.

9. The mass of a photon with wavelength 3.6 Å is _____________
a) 3.139 X 10-33 kg
b) 4.139 X 10-33 kg
c) 5.139 X 10-33 kg
d) 6.139 X 10-33 kg
View Answer

Answer: d
Explanation: Here, wavelength = 3.6 X 10-10 m
Velocity of photon = velocity of light
Mass, m = h/λv = 6.139 X 10-33 kg.

10. Which phenomenon is shown by the following diagram?
Secondary Rainbow formation phenomenon is shown by the following diagram
a) Scattering of light
b) Dispersion of light
c) Primary Rainbow Formation
d) Secondary Rainbow formation
View Answer

Answer: d
Explanation: In the case of secondary rainbow formation, the light rays undergo internal reflection twice inside the drop. The intensity of light, in this case is, reduced. Also, the order of the colors is reversed as shown in the figure.

Sanfoundry Global Education & Learning Series – Engineering Physics.

To practice all areas of Engineering Physics, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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