2.1 (i)

Demonstration 1

Firstly it is worth discussing the historical basis to Young's Double Slits experiment. Set up the Young's double slit experiment with a monochromatic LASER.

Analysis

It is worth discussing the observations and recording the observations in terms of positions of maxima and the dimensions of the set up, as well as the intensity variation. You may wish to do the complete analysis of the experiment here, using the equation to find a value of λ and checking it is in the correct part of the visible spectrum.

Demonstration 2

Having recently seen diffraction with the microwave kit, they should be able to predict what will happen with two slits. Set up the microwave apparatus so that you (they) can plot out points of maxima and minima along an arc.

Analysis

With the maxima and minima plotted out, they can then calculate path difference. It can also be explained using the Young's slits sliding waves (black background). They can then compare this to a calculated value of λ from information taken from the set up. This can all be compared to a value for λ from the microwave kit; usually 2.8 cm.

Demonstration 3

They have already seen the two source interference pattern in 2.1 (h). It is very difficult to get a single source to diffract through two slits and then observe the resulting pattern, as the amplitude of the waves are greatly decreased as they pass through the slits; but it is worth having a go.

Demonstration 4

You can use two speakers separate on a line playing a single frequency. You then use a microphone to find spots of maxima and minima. It is useful to revise the double-slit interference equation and the concept of path difference. Get the pupils to walk around and find positions of maxima and minima - it is useful to discuss path difference, phase difference and what happens when you listen with both ears.

Demonstration 5

As an extension, you can use the LASER and diffract the light around the tip of a pin and observe the fringes.

Syllabus

Waves & Particles