Question

The ratio of the intensity at the centre of a bright fringe to the intensity at a point one-quarter of the distance between two fringes from the centre is

• A. 2
• B. ½
• C. 4
• D. 16

Answer 1

Answer: (D)

16

Answer 2

sin i = µ sin r … (1)

differentiating eq. (1) cos i di = µ cos r dr

or $\frac { \mathrm { dr } } { \mathrm { di } }$ = $\frac { \cos i } { \mu \cos r }$ =$\frac { 1 } { 2 }$

or 2 cos i = µ cos r

or 4 cos² i = µ² cos² r = µ² (1 – sin² r)

or 4 cos² i = µ²= µ² – (1 – cos² i)

or 3 cos² i = µ² – 1

or cos i =$\sqrt { \frac { 7 } { 27 } }$

or cos i =$\sqrt { .26 }$= .5

or i = 60⁰.