Question

Light illuminates two closely spaced thin slits and produces an interference pattern on a screen behind. How will the distance between the fringes of the pattern differ for red light and blue light? 1. The same spacing for both 2. Closer for red light 3. Farther apart for red light

Answer 1

Answer:

3. Farther apart for red light

Explanation:

The distance $y$ between fringes is

$y = \dfrac{\lambda L }{d},$

where $\lambda$ is the wavelength of light, $L$ is the distance to the screen, and $d$ is the slit separation.

Now, the wavelength $\lambda_r$ of the red light is greater than for the wavelength $\lambda_b$ for blue light:

$\lambda_r> \lambda_b$,

which means

$\dfrac{\lambda_r L }{d}>\dfrac{\lambda_b L }{d},$

In other words, the distance between the fringes is greater for red light, which from the options is choice 3.