Question

2.DVD players use red lasers with a wavelength of 650 nm, while Blu-ray players use blue lasers (hence the name) with a wavelength of 405 nm.
1. Which color would need a larger double slit spacing d to produce an interference pattern that has the first maxima 1 mm from the central bright spot?

Answer 1

Answer:

Blue light

Explanation:

For maxima interference we have the relation

$dsin\theta=m$

where

m =  order

d = Slit gap

we have the relation

$\dfrac{dy}{D}=\lambda$

y = First maxima =  1 mm (fixed)

D = Distance to screen = 1 m (fixed)

So, the wavelength $(\lambda)$ needed should be larger.

Hence, the blue light which has higher wavelength of 650 nm is to be used as it requires larger double slit spacing.