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. 6000 Å
B. 4200 Å
C. 3000 Å
D. 1800 Å

Answer

B

Explanation

Angular width `beta= (2lambda)/(a)implies beta prop lambda`
`(beta_(1))/(beta_(2))= (lambda_(1))/(lambda_(2))= (beta)/((70)/(100)beta)= (6000)/(lambda_(2))implies lambda_(2)= 4200 Å`