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

500 nm

Step-by-step 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=(1)/(d)=(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=(d sin \theta)/(m)=((2\cdot 10^(-6))(sin 30^(\circ)))/(2)=5\cdot 10^(-7) m = 500 nm`