# Physics Questions and Answers – Wave Optics – Refraction and Reflection of Plane Waves Using Huygen’s Principle

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This set of Physics Objective Questions and Answers for Class 12 focuses on “Wave Optics – Refraction and Reflection of Plane Waves Using Huygen’s Principle”.

1. The speed of the yellow light in a certain liquid is 2.4 × 108 m/s. Find the refractive index of the liquid.
a) 6.25
b) 5.73
c) 1.25
d) 9.73

Explanation: μ = $$\frac {c}{v_t}$$
μ = 3 × $$\frac {10^8}{2.4}$$ × 108
μ = 1.25

2. The wavelength of light coming from a sodium source is 589 nm. What will be its wavelength in the water?
a) 625 nm
b) 443 nm
c) 789 nm
d) 125 nm

Explanation: λ = 589 nm, μ = 1.33.
Wavelength in water, λW = $$\frac {\lambda }{\mu }$$
λW = $$\frac {589}{1.33}$$
λW = 443 nm.

3. A light wave enters from air into glass. How will the energy of the wave be affected?
a) Decreases
b) Increases
c) Remains the same
d) Independent

Explanation: When a light wave enters from the air medium into the glass medium, the energy of the wave decreases because a part of the light wave is reflected in the air. Therefore, in this way, energy will be affected.

4. If a wave undergoes refraction, what will be the phase change?
a) 180o
b) 270o
c) 90o
d) 0o

Explanation: When a wave undergoes refraction, the phase change will be zero. The phase change is what guides the process. Therefore, no phase change occurs to a wave during refraction.

5. When a wave undergoes reflection at a denser medium, what will be the phase change?
b) 0

Explanation: When a wave is reflected in the rarer medium from the surface of a denser medium, it undergoes a phase change of π radian. Therefore, when a wave undergoes reflection at a denser medium, the phase change will be π radian.

6. Two wave-fronts intersect each other.
a) True
b) False

Explanation: No, this statement is false. If they intersect, then there will be two rays or two directions of propagation of energy at the point of intersection which is not possible. Therefore, two wave-fronts do not intersect with each other.

7. A light wave enters from air into glass. How will the frequency of the wave be affected?
a) Increases
b) Remains unchanged
c) Decreases
d) Insignificant

Explanation: The frequency of the wave remains unchanged. This is because the frequency is independent of the wave dynamics. Therefore, when a light wave enters from the air medium into the glass medium, the frequency will be the same.

Sanfoundry Global Education & Learning Series – Physics – Class 12.

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