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 wavelength $λ$ . In another experiment with the same set up the two slits are of equal amplitude A and wavelength $λ$ but are incoherent. The ratio of the intensity of light at the mid-point of the screen in the first case to that in the second case is

Moderate

A

1 : 2
B

2 : 1
C

4 : 1
D

1 : 1

Solution

Resultant intensity $I = I_{1} + I_{2} + 2 \sqrt{I_{1} I_{2}} cosφ$
At central position with coherent source (and
$I_{1} = I_{2} = I_{0}$
$I_{con} = 4 I_{0} - - - - - (ii)$
In case of incoherent at a given point, $ϕ$ varies randomly with time so (cos f)_av = 0
$I_{In coh} = I_{1} + I_{2} = 2 I_{0} - - - - - (ii)$
Hence $\frac{I_{coh}}{I_{Incoh}} = \frac{2}{1}$

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