Question

A light of wavelength $6000\mathring{A}$ is incident normally on a grating $0.005m$ wide with $2500$ lines. Then the maximum order is :

• A. $1$
• B. $3$
• C. $2$
• D. $4$

Answer 1

The correct option is B $3$

Length of grating is $0.005/2500=2\times {10}^{-6}m$

Now,

$m\lambda =e$ (for maximum order)

$m\times 6000A^0=2\times {10}^{-6}$

$m=3$