A slit of width a is illuminated by red light of wavelength `6500Å`. If the first minimum falls at `theta=30^(@)`, the value of a is

Options

A. A)`6.5xx10^(-4)mm`
B. B)1.3 micron
C. C)`3250Å`
D. D)`2.6xx10^(-4)cm`

Answer

B

Explanation

According to principle of diffraction
`asintheta=nlambda`
where n = order of secondary minimum
`therefore asin30^(@)=1xx(6500xx10^(-10))`
or `a=1.3xx10^(-6)m`
or `a=1.3` micron