Angular width of central maxima in the Fraunhofer diffraction pattern of a slit is measured. The slit is illuminated by light of wavelength `6000Å`. When the slit is illuminated by light of another wavelength, the angular width decreases by 30%. The wavelength of this light will be

Options

A. (a) `6000Å`
B. (b) `4200Å`
C. (c) `3000Å`
D. (d) `1800Å`

Answer

B

Explanation

Angular width `beta=(2lambda)/(d)`
`impliesbeta_1/beta_2=lambda_1/lambda_2implies(beta)/(70/100beta)=(6000)/(lambda_2)implieslambda_2=4200Å`