Module 4 - Section 2 - Diffraction Gratings

Question 1

What happens when you diffract light through more slits ?

Answer 1

Interference patterns get sharper when you diffract through more slits

Question 2

What happens if you repeat the double slit experiment but just with more slits ?

Answer 2

You basically get the same shaped pattern as for 2 slits but the light fringes are more brighter and narrower and the dark fringes are more darker

When the monochromatic light ( one wavelength ) gets passed through a diffraction grating with hundreds of slits per millimetre - the interference pattern gets very sharp - because there are so many beams reinforcing the pattern

Question 3

Why do more slits equal much sharper fringes ?

Answer 3

because there are so many beams reinforcing the pattern

Question 4

Why should you do the double slit experiment with more slits ?

Answer 4

because sharper fringes mean more precise measurements as they are easier to tell apart and so are easier to measure

Question 5

Whats a maxima ?

Answer 5

It’s the light fringe basically - it’s when there is constructive interference and the two waves displacement adds to gather to make a maximum displacement is called a maxima.

Question 6

Whats the zero order line ?

Answer 6

It’s the line of maximum brightness at the centre

Question 7

What are the lines either side of the zero order line called ?

Answer 7

1st order lines then either side of that are called the 2nd order lines

Question 8

Why is it with monochromatic light it is easier to measure the distance between the maxima ?

Answer 8

Because monochromatic light makes sharp maxima lines so it’s easier to measure

Question 9

What n does the first order and the third order of have ?

Answer 9

They have n=1 and n=3

Simple

Question 10

What does shining white light through a diffraction grating produce ?

Answer 10

It produces Spectra ?

Question 11

Why does shining white light through a diffraction grating produce a spectra ?

Answer 11

This is because white light is really a mixture of colours - if you diffract white light through a grating then the patterns are due to the different wavelengths within the white light being spread out by different amounts

Each order becomes a spectrum with red on the outside and violet on the inside - the zero - order maximum though - stays white because al the wavelengths just pass straight through