Question

Seberkas cahaya monokromatik dijatuhkan pada kisi difraksi dengan 5000 goresan/cm menghasilkan spectrum garis terang orde kedua membentuk sudut 30 derajat terhadap garis normalnya. Panjang gelombang cahaya yang digunakan adalah …. *

Answer 1

Answer:

500 nm

Explanation:

In this problem, we have a diffraction pattern created by light passing through a diffraction grating.

The formula to find a maximum in the pattern produced by a diffraction grating is the following:

$d sin \theta = m\lambda$

where:

d is the distance between the lines in the grating

$\theta$ is the angle at which the maximum is located

m is the order of the maximum

$\lambda$ is the wavelength of the light used

In this problem we have:

$\theta=30^{\circ}$ is the angle at which is located the 2nd-order bright line, which is the 2nd maximum

n = 5000 lines/cm is the number of lines per centimetre, so the distance between two lines is

$d=\frac{1}{d}=\frac{1}{5000}=2\cdot 10^{-4} cm = 2\cdot 10^{-6} m$

Re-arranging the equation for $\lambda$, we find the wavelength of the light used:

$\lambda=\frac{d sin \theta}{m}=\frac{(2\cdot 10^{-6})(sin 30^{\circ})}{2}=5\cdot 10^{-7} m = 500 nm$