Question

A 17-mm-wide diffraction grating has rulings of 530 lines per millimeter. White light is incident normally on the grating. What is the longest wavelength that forms an intensity maximum in the fifth order

Answer 1

Answer:

377 nm

Explanation:

Number of lines per meter is, $N &=530 \times 1000 \\ &=530000 \text { lines } / \mathrm{m} \end{aligned}$

Grating element is, $d=\frac{1}{N}$

$=1.8868 \times 10^{-6} \mathrm{~m}[tex]

Order is, n=5

Condition for maximum intensity is, [tex]d \sin \theta=n \lambda$

 $\lambda &=\frac{1.8868 \times 10^{-6}}{5(\sin 90)} \\ &=0.377 \times 10^{-6} \mathrm{~m} \\ &=377 \mathrm{~nm}$