5CH - Past papers by topic

Questions for Mechanics and Electricity. Radiation to follow.

You can download these or view them online.

5CH - Multiple slit diffraction grating

As we already know, a diffraction grating can be used to produce interference in the same way a double slit can. We looked at how we can use our knowledge of path difference with a bit of trigonometry to give us an equation for use with diffraction gratings. This gave us the equation nλ = d sinθ where n is the order of the maxima e.g. 1,2,3 etc. This equation can also be applied to the path difference for a minima but I haven't seen this asked for some time.

To calculate the slit separation, d,  you must know firstly how many lines there are per metre and then divide 1 by that value. The angle of deviation, θ, is the angle that the wave/ray is deviated from the normal line.

Remember also that wavelength of red light = 700 nm and wavelength of violet light = 400 nm.

5CH - Path difference

As we saw today, path difference is what causes interference. The path difference is the difference in distance travelled by the waves. This difference in distance will mean that the waves become either in phase or out of phase. Waves that arrive in phase will interfere constructively and waves that arrive out of phase will interfere destructively.

We introduced two equations for working with path difference, one for maxima and one for minima. You need to be able to select the correct one for the given situation. Remember of course that the path difference equation for a minima isn't actually very useful! It might be best to use p.d. = (n - 1/2)λ.

This will not be given in the data booklet though.

5CH - Interference of light

Light can undergo interference as well. You can use a diffraction grating to make this happen. You need to be able to explain an interference pattern of bright and dark areas, you also need to know the differences between white light through a prism and white light through a diffraction grating.

5CH - Interference

Looked at interference today. Interference is caused by two or more waves getting in each others way. When they meet they produce either constructive or destructive interference. What these are is explained in the video. All wave types - sound, light etc. exhibit interference patterns which are made up of alternating lines of constructive and destructive interference.

5CH - Ray diagrams

Applied the refraction formula to drawing/completing ray diagrams today. You can use the refractive index formula along with the knowledge that the angles in a triangle add up to 180 degrees to figure out how light will pass through most objects.

Sometimes we will have to consider the critical angle when completing ray diagrams. If the angle of incidence is greater than the critical angle then the light will reflect. The angle of reflection in these cases is equal to the angle of incidence.

Note: The more observant will spot my mistake with the angles. They should be 54 and 36 not 34 and 56. Final answer is still correct.

5CH - Critical angle and internal reflection

Not all light will be refracted through materials such as glass. Materials like glass have the ability to internally reflect light if the ray is at a certain angle. This is called the critical angle and is the angle beyond which no refraction will take place. In other words, the light will not pass through the material but be reflected back in the original direction of the ray.

Remember that at the precise point of the critical angle, the ray of light refracts into the air at 90 degrees. This is the last refraction that occurs before all light is reflected. Recall also that the angle of incidence is always equal to the angle of reflection.