The inverse square law Essay

Published: 2019-12-06 06:42:10
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Category: Law

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The inverse square law would mean that we should get a graph (predicted) as shown below. [Graph of y = 1/x2] What this means in scientific terms is that photons (small packets of light energy) usually hit a solar cell and sometimes dislodge electrons from the semiconductor, into motion inducing a small current. As the distance increases between the solar cell and the light bulb the same number of photons are spread out over an area of an imaginary sphere, which expands in proportion to the square of the distance.

It therefore means, as distance varies the inverse of the distance squared proportion of photons hit a unit of area per second and thats why the amount of current produced should also have the same relationship. Power- Power is a much simpler factor when it comes to light intensity. As the Intensity = Power/area(constant). This means that the increase light intensity is proportional to the increase in power, given that the distance is constant. This will provide a y = m. x + c line on a graph as shown below. [Graph]

In scientific terms this means that there will be more photons generated by the light bulb per second therefore meaning that there will be more photons hitting a specific unit area per second. The correlation should be proportional. Skill Area O: Obtaining evidence Activities chosen should enable pupils to develop their abilities in the aspects listed below.  Use the equipment to perform the practical in an appropriate way to meet the demands of the activity.  Pay proper regard to safety precautions in the way in which the equipment is used.

Make an appropriate number of observations or measurements to meet the requirements of the activity. Record the observations or measurements in a clear way.  Recognise the need for precision and accuracy when observing or measuring.  Repeat observations or measurements when necessary.  Recognise the need for reliable evidence. Candidates should be taught: a to use a range of apparatus and equipment safely and with skill; b to make observations and measurements to a degree of precision appropriate to the context; c to make sufficient relevant observations and measurements for reliable evidence; d to consider uncertainties in measurements and observations; e to repeat measurements and observations when appropriate; f to record evidence clearly and appropriately as they carry out the work.


The mark descriptions are designed to be hierarchical. 6 marks O. 6a make sufficient systematic and accurate observations or measurements and repeat them when appropriate  Use your equipment to obtain the results as accurately as possible. * Make sure your results are spread out over a good range.  Make sure that you have enough results to allow you to draw a conclusion.

V power supply 25W tungsten filament bulb with lamp Low efficiency Solar cell Ruler Analogue Ammeter Analogue Voltmeter Analogue Milliammeter Method: The apparatus will be connected up as shown below. [Circuit diagrams] As I predict light intensity will decrease rapidly as the distance between the bulb and cell increases, we must have a rather small range.

When testing the effect of distance I connect up the circuit and establish what the constant power output is, then I will take readings from the Milliammeter every time I move the solar cell 1cm from 0-15 cm. This will give us plenty of readings so I can easily establish a pattern in the experiment. When testing the effect of the power input I plan to hold the cell 1cm away from the bulb (this will give relative high readings), then move the knob on the rheostat a few centimetres (to increase resistance) and then take readings from the voltmeter and the ammeter (multiplying the two would give power input in Watts).

Both experiments will be repeated to increase the accuracy but not averaged as there are too many variables. Fair Test- In order to make it a fair test we try to keep the two other factors constant while the other is being tested. This included maintaining white light being generated by the light bulb throughout, maintaining constant power output using accurate readings of volt/ammeters (when varying distance) and keeping the distance between the bulb and the solar cell at 1 cm (when varying power).

Background radiation and reflections of the white light could cause anomalies in the data so it is important to keep the conditions constant, i. e. the same number of lights on in the lab. Over-heating of the bulb (causing increase in resistance) and the solar cell (resulting in fall of resistance) are also sources of error but are mainly unavoidable with the time constraints, but the power will not be turned on until its necessary to obtain a reading.

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