Red light of wavelength `5400 Å` from a distant source modulated wave of `60%` modulattion by using a condenser of capacity 250 pF in parallel with a load resistnce `100kOmega`. Find the maximum modulated frequency which could be detected by it.

Options

A. 1.89 mm
B. 4mm
C. 1 mm
D. 3mm

Answer

A

Explanation

Here, wavelength `lambda = 5400Å=5.4 xx 10^(-7)`m,
a=0.80 mm = `8 xx10^(-4)`m, D=1.4m
`therefore` Distance between first two dark bands on each side of central maximum is the width of central maximum
`=2x = (2lambdaD)/d = (2 xx 5.4 xx 10^(-7) xx 1.4)/(8 xx 10^(-4))`
`=1.89 xx 10^(-3)` m =p1.89 m