The practical issues at hand here, are far less complicated than that of the Gamma radiation experiment. We have a limited amount of resources available. I could have constructed an LDR circuit attached to a ohm meter, this would gage the changing resistance of the circuit as the light source is moved away. However this is impractical, and although would prove an inverses square relationship it doesn’t deal in the basic units. In order to get a direct reading of the changing lux readings it would be sensible to use a light sensor and a large analogue meter meter.
I will use a Griffin and George ray box with 12v bulb as the source of light. The only real decision to be made here is what form of measurement device is to be used to measure the distance of the source for the dector. I have decided to measure roughly over 25 cm, this means I simply cannot use either the digital, or sight-read vernier callipers, as they have a range only up to 15 cm. So I must use a metre rule. Methods The experiment is very similar to the Gamma experiment, in that you are moving a point source away from a dector at steady intervals.
The only complex detail was ensure the ray of light pointed directly at the centre of the dector, which can be done simply by sight, by looking at it and ensuring that it is pointing at the centre. The dector will be held in a clamp at the level of the filament lamp, and again a metre rule will be taped to the desk, in which the light box will be ‘braced’ against, I will then move it way from the dector in intervals of 1 cm over a range of 25 cm, no repeats are needed, not because accuracy isn’t essential but the wave is fundamentally different.
With the gamma we had to wait for it to decay, light however does not decay it emits a constant stream of photons, so the level of light intensity will be the same from one second to the next. What is essential is to take a ‘background count’ of ambient light; simply leaving the light dector will do this. (See appendix for results and graph of trial experiments. ) Conclusion of trial experiments My trial experiments have helped define which of the electromagnetic waves I will investigate closer in the main experiment.
I have chosen to further investigate the area of the electromagnetic spectrum with wavelengths starching from 10-10 m to 10-13 m, better known as Gamma radiation. My experimental results for light were much better than those of Gamma, and this is precisely why I want to further investigate Gamma radiation. I have already proved that the inverse square law holds for Light radiation, this is shown on the graph in which I plotted distance against intensity in Lux’s. It proved a curve, with a constant half-life.
This shows that when the distance is doubled, the intensity halves. So I have already proved the inverse square law is correct for light, so there is nothing else to do. I feel my relatively poor results with Gamma radiation are not due to poor experimental techniques, or that it simply doesn’t obey the inverse square law, but due to the weakness of the Gamma radiation source. As you see on the graph of distance against the reciprocal of the square root of the count, it is a straight line up to a distance of about 40mm then it ceases to show a correlation.
If you look at my table of results you will see that at around the distance of 40mm the radiation count drops to a level almost equal to that of the background count. So any results after this point are not reliable. So in order to prove that Gamma radiation, and all members of the electromagnetic spectrum, obey the inverse square law I will merely have to work over a distance up to, but not beyond about 30mm. This will mean having to take readings with smaller distances in-between so will facilitate the need for the usage of the digital vernier scale callipers, as they have a higher level of accuracy.