4H - Specific heat capacity (Homework out)

After carrying out an experiment to determine how well different metals heat up we related this to the idea of specific heat capacity. In simple terms this is a measure of how good a substance is at heating up or cooling down. This lead us to an equation for specific heat capacity and a few worked examples. Past paper on specific heat capacity for Tuesday.

5CH - Photoemissions

Photoemission is the release of electrons from a material. Whether an electron is released or not depends upon the frequency of the radiation hitting the material not the irradiance. This leads us to the idea that light and other types of electromagnetic radiation are made up of tiny particles called photons. The energy that these photons have is directly proportional to their frequency as stated in the the equation E = hf.

5CH - Irradiance

Irradiance is the power of radiation per unit area. The closer you are to a source of radiation, the greater the irradiance. As you move away from the source the irradiance will decrease, in other words there is less radiation per unit area. If you continue to move away from a radiation source then the irradiance will reduce as the square of the distance from the source. This means that if you double the distance from the source of radiation then the irradiance will be four times less.

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.