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Light of Wavelength 5000 å Falls on a Plane Reflecting Surface. What Are the Wavelength and Frequency of the Reflected Light? for What Angle of Incidence is the Reflected Ray Normal to the Incident Ray? - CBSE (Science) Class 12 - Physics

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Question

Light of wavelength 5000 Å falls on a plane reflecting surface. What are the wavelength and frequency of the reflected light? For what angle of incidence is the reflected ray normal to the incident ray?

Solution

Wavelength of incident light, λ = 5000 Å = 5000 × 10−10 m

Speed of light, c = 3 × 108 m

Frequency of incident light is given by the relation,

`v = c/lambda`

`= (3xx10^8)/(5000xx10^(-10)) = 6xx 10^14 Hz`

The wavelength and frequency of incident light is the same as that of reflected ray. Hence, the wavelength of reflected light is 5000 Å and its frequency is 6 × 1014 Hz.

When reflected ray is normal to incident ray, the sum of the angle of incidence, `anglei` and angle of reflection, `angler` is 90°.

According to the law of reflection, the angle of incidence is always equal to the angle of reflection. Hence, we can write the sum as:

`anglei + angler = 90`

`anglei + anglei = 90`

`anglei = 90/2 = 45^@`

Therefore, the angle of incidence for the given condition is 45°.

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Solution Light of Wavelength 5000 å Falls on a Plane Reflecting Surface. What Are the Wavelength and Frequency of the Reflected Light? for What Angle of Incidence is the Reflected Ray Normal to the Incident Ray? Concept: Refraction and Reflection of Plane Waves Using Huygens Principle - Reflection of a Plane Wave by a Plane Surface.
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