In the Young's experiment, one of the slit is covered with a transparent sheet of thickness `3.6xx10^(-3)` cm due to which position of central fringe shifts to a position originally occupied by 30th bright fringe. The refractive index of the sheet, if `lambda=6000Å` is

Options

A. 1.5
B. 1.2
C. 1.3
D. 1.7

Answer

A

Explanation

The position of 30th bright fringe, `y_(30)=(30lambdaD)/(d)`
Now, position shift to central fringe is, `y_(0)=(30lambdaD)/(d)`
But we know `y_(0)=(D)/(d)(mu-1)t`
`rArr (30lambdaD)/(d)=(D)/(d)(mu-1)t`
`rArr (mu-1)=(30lambda)/(t)=(30xx6000xx10^(-10))/(3.6xx10^(-5))=0.5`
`rArr mu=1.5`