Question

One of the two slits in YDSE is painted over, so that it transmits only light waves having intensity half of the intensity of the light waves having half of the intensity of the light waves through the other slit. As a result of this

• A. fringe pattern disappears
• B. bright fringes become brighten and dark ones become darker
• C. dark and bright fringes get fainter
• D. dark fringes get brighter and bright fringes get darker

Answer 1

The correct option is D dark fringes get brighter and bright fringes get darker

Case 1: When slit are of equal width, if $I_o$ is intensity of light then,

$I_{max}=I_o+I_o+2\sqrt{I_o{I}_o}=4I_o$

$I_{min}=I_o+I_o-2\sqrt{I_o{I}_o}=0$

Case 2: When one of the slit is painted over, its intensity would reduce to half then,

$I_{newmax}=I_o/2+I_o+2\sqrt{I_o{I}_o/2}=2.932I_o$

$I_{newmin}=I_o/2+I_o-2\sqrt{I_o{I}_o/2}=0.068I_o$

Therefore, dark fringes get brighter and bright fringes get darker