Paper 3: Required practical 2 - Interference effects

Question 1

Why should the screen you display the interference pattern on have a matt finish?

Answer 1

Reduce the likelihood of the laser beam reflecting from the screen into someone’s eye and causing harm

Question 2

How should you measure the fringe spacing of an interference pattern?

Answer 2

Measure across a large number of fringes and then divide by the number of spaces measured across
Make sure to divide by the number of fringe spaces NOT fringes

Question 3

What equipment could you use to measure the slit separation?

Answer 3

Vernier Calliper

Question 4

How can the wavelength of the laser be determined from a graph of fringe width against the distance from the screen?

Answer 4

The gradient of the graph will be w/D and so multiplying the gradient by the slit separation you will obtain the wavelength

Question 5

How is the diffraction grating spacing calculated?

Answer 5

The reciprocal of the number of lines per metre

Question 6

How does a diffracton pattern from a double slit experiment compare to one from a diffraction grating?

Answer 6

As the number of slits increases, the pattern becomes sharper and the brightness of the fringes increases - more rays are reinforcing the pattern