Ncert Exercises & Solutions

10.9 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?

Hint: $\nu=\frac{c}{\lambda } $

Step 1: Find the frequency of incident light.
Wavelength of incident light, $λ$ = 5000 $\overset{o}{A}$ = 5000 x 10^-10 m
Speed of light, c =3 x 10⁸ m
Use the following relation for the frequency of incident light:

$v = \frac{c}{λ} = \frac{3 \times 10^{8}}{5000 \times 10^{- 10}} = 6 \times 10^{14} Hz$

Step 2: Find the wavelength and frequency of the reflected light.
The wavelength and frequency of incident light are equal to the reflected ray.
Step 3: Find the angle of incidence.
When the reflected ray is normal to the incident ray, the sum of the angle of incidence, $∠ i$ and angle of reflection, $∠ r$ is 90°.
From laws of reflection, we know that the angle of incidence is always equal to the angle of reflection

\begin{array}{l} ∠ i + ∠ r = 90 \\ ∠ i + ∠ i = 90 \\ ∠ i = \frac{90}{2} = 45^{\circ} \end{array}

Therefore, 45° is the angle of incidence.

NEET Information

courses

Company

Botany Questions

Chemistry Questions

Physics Questions

Zoology Questions