Question

(waves class)

please answer the questions in the following order:

1. if you were shown three different interference patterns (double slit, single slit, and diffraction grating), how could you tell the difference between them?

2. Newton thought that light wasnt a wave because he couldn’t see diffraction or interference. Imagine you are transported back in time to convince him otherwise. Write a 1-2 paragraph explanation for Newton explaining why he does not see these features despite the wave of natural light.

please answer both questions. thank you a million !

Answer 1

1 .

Let us understand the difference between Single Slit , Double Slit and Diffraction Grating

In a single slit diffraction, light spreads out in a line perpendicular to the slit. No particular interesting phenomena are observed.

But in a double slit diffraction, light diffracts when passing though the slits, but the light waves coming out from those slits interfere with each other to produce an interference pattern on the screen. The light is spread out in a line, like in the single slit, but here there is interference, producing regions of constructive (bright fringes) and destructive (dark fringes) interference and a very bright spot at the middle of the screen, called the central maxima.

So, looking at diffraction only, there is no difference between single slit and double slit because in both cases diffraction happen; but in a double slit there is diffraction as well as interference among the diffracted rays.

But a diffraction grating concentrates all the light for a given frequency into one (or at most a handful), of angular positions. So you read one bright, narrow line in the output spectrum and you’re done.

2.

He thought the wave theory predicted that the interference pattern would be bright in the middle, so that when it was observed to be dark in the middle, that falsified the wave theory. He was mistaken because he didn't understand that a reflected wave could be inverted