First slide

Coherent sources and their importance in interference

Question

In Young’s double slit experiment, the two slits act as coherent sources of equal amplitude a and of wave length $λ$ . In other experiment with the same set up, the two slits are sources of equal amplitude a and wavelength ‘ $λ$ ’ but are incoherent. The ratio of intensity of light at the midpoint of the screen in the first case to that in the second case is

Moderate

A

2:1
B

1:2
C

3:4
D

4:3

Solution

Given
Amplitude $= a$
Wave length $= λ$
When sources are coherent, intensity at mid-point
$I_{\max} = {(a_{1} + a_{2})}^{2}$
$\Rightarrow I_{\max} = {(a + a)}^{2} = 4 a^{2}$
When sources are incoherent, no interference occurs.
Intensity at mid point,
$I = I_{1} + I_{2} = a^{2} + a^{2} = 2 a^{2}$
$∴ \frac{I_{\max}}{I} = \frac{4 a^{2}}{2 a^{2}} = 2 : 1$
Therefore, the correct answer is (A).

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App