Question

A single-slit diffraction pattern is formed on a distant screen. Assume the angles involved are small. Part A By what factor will the width of the central bright spot on the screen change if the wavelength is doubled

Answer 1

If the wavelength is doubled, the width of the central bright spot on the screen will increase by a factor of 2 (that is, it will also double).

Step-by-step explanation:

For a single-slit diffraction, diffraction patterns are found at angles θ for which

w sinθ = mλ

where w is the width

λ is wavelength

m is an integer, m = 1,2,3, ....

From the equation, w sinθ = mλ

For the first case, where nothing was changed

w₁ = mλ₁ / sinθ

Now, If the wavelength is doubled, that is, λ₂ = 2λ₁

The equation becomes

w₂ = mλ₂ / sinθ

Then, w₂ = m(2λ₁) / sinθ

w₂ = 2(mλ₁) / sinθ

Recall that, w₁ = mλ₁ / sinθ

Therefore, w₂ = 2w₁

Hence, If the wavelength is doubled, the width of the central bright spot on the screen will increase by a factor of 2 (that is, it will also double).