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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

ConceptRefraction and Reflection of Plane Waves Using Huygens Principle Reflection of a Plane Wave by a Plane Surface

#### 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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