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# Skill Area P - Planning experimental procedures.

Extracts from this document...

Introduction

Solar cell investigation

Skill Area P: Planning experimental procedures

Activities chosen should enable pupils to develop their abilities in the aspects listed below.

1. Plan the most appropriate experimental method that can be carried out in a school science context.
1. Identify and take account of the key safety requirements.
1. Select the most appropriate measuring instruments and other necessary equipment.
1. Consider how many results to take and whether repetition is necessary.
1. Consider over what range the results should be taken.
1. Plan how to vary, control or take account of the key factors likely to affect the outcome of the activity.
1. Make predictions where this helps the planning or supports their understanding of the nature of the Enquirer.
1. Make use of scientific knowledge and understanding to explain the plans made.
1. Use secondary sources or preliminary work as an aid to planning.

Aim:         To investigate the effects of two variables on solar cell output.

Factors:

Factor’ here means ‘anything which may influence the outcome of the activity’ e.g. guarding against draughts, avoiding heating effects, keeping temperature constant, or changing a variable.

It may not always be appropriate - or possible - to change or control such factors, but where they are included in mark descriptions, candidates should consider the things which may influence the result.

Candidates should be taught:

a         to use scientific knowledge and understanding, drawing on secondary sources where appropriate, to turn ideas suggested to them, and their own ideas, into a form that can be investigated;

b         to carry out preliminary work where this helps to clarify what they have to do;

c         to make predictions where it is appropriate to do so;

d         to consider the key factors in contexts involving a number of factors;

e         to plan how to vary or control key variables;

f

Middle

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.

1. Use the equipment to perform the practical in an appropriate way to meet the demands of the activity.
1. Pay proper regard to safety precautions in the way in which the equipment is used.
1. Make an appropriate number of observations or measurements to meet the requirements of the activity.
1. Record the observations or measurements in a clear way.
1. Recognise the need for precision and accuracy when observing or measuring.
1. Repeat observations or measurements when necessary.
1. 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.

MARK DESCRIPTIONS:        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

1. Use your equipment to obtain the results as accurately as possible.

Conclusion

The two graphs show a nearly straight correlation but a very slight curve a little like a y=x2 curve.

The curve of the graphs are more likely to have equation of around y = x1·5.

Conclusion:

From plotting the graphs and analysing them we can conclude various points.

After analysing the graphs of solar cell output and √1/cell output against distance, we can establish that there is evidence of inverse square law.

That is to say that the √1/cell output gives a straight line when plotted against distance, which is the same as plotting solar cell output against 1/distance2.

In other words there is evidence to suggest that solar cell output is proportional to the inverse square of the distance between the cell and the bulb.

This trend was predicted in the hypothesis: Solar cell output will have a 1/x2 relationship with distance. Therefore we can evidently see that the hypothesis regarding the relationship between solar cell output and distance has been fully supported.

The reason for this relationship is that light spreads out in an ever-expanding spherical shape.

The surface area of the sphere increases in proportion to the square of the increase of distance between the cell and the bulb.

But as area is the variable denominator in the intensity formula, it means that if area doubles intensity would halve.

However, according to our first point there is a square relationship with area and distance, meaning if distance is doubled, area will be quadrupled and intensity would be quartered.

Hence giving us inverse square law.

This can be explained scientifically.

The same number of photons of light are being emitted per second (as power is constant) by the bulb.

But as the distance between the cell and bulb is increasing, the area of where the photons are hitting is increasing by the square of the distance, hence only the inverse squared number of photons are hitting the cell every second as the distance increases.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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