Question

Column I shows the changes introduced in Young's double-slit experiment while Column II tells the changes in the fringe pattern while performing the experiment. Match each situation given in Column I with the result given in Column II.

Column I		Column II
A	If sodium light is replaced by red light of same intensity	1	All fringes are coloured except central fringe
B	Monochromatic light is replaced by white light	2	Fringe width will became quadrupled
C	Distance between slits and screen is doubled and the distance betwen slits is halved	3	The bright fringe will bocame less bright
D	If one of the slits is covered by cellophone paper	4	The fringe width will increase

• A. A-(4), B-(1), C-(2), D-(3)
• B. A-(1), B-(2), C-(3), D-(4)
• C. A-(2), B-(3), C-(1), D-(4)
• D. A-(3), B-(2), C-(4), D-(1)

Answer 1

Answer: (A)

Fringe width, $W=\frac{D \lambda}{d}$
where, $D=$ distance between slits and screen
$d=$ distance between slits and
$\lambda=$ wavelength of light
A. $\lambda$ increase so $W$ also increase
$(\therefore A \rightarrow 4)$
B. White light produces coloured fringes $(\because B \rightarrow 1)$
C. If $D$ is doubled and $d$ is halved, then $W$ becomes four times
$(\because C \rightarrow 2)$
D. If intensity of either slit is reduced, the bright fringes became less bright.
$(\because D \rightarrow 3)$