Physics Controlled Assessment

You will be assessed in 3 parts:-1. Part A – Planning (18 marks)2. Part B – Observations (6 marks)3. Part C – Conclusions (24 marks)

This will count for 25% of your overall GCSE Physics Grade.

How is it assessed?

This controlled assessment is about how the resistance of a LDR changes with the brightness of a lamp.

Student Brief

You will need to plan an investigation to test how the resistance of a LDR changes with the current flowing through the lamp which is illuminating the LDR.

Part A- Planning

A LDR Lamp Ammeter Variable DC Power pack Leads/wires Cardboard tube Ohmmeter

You will be given the following equipment:-

A hypothesis that you are planning to test An explanation of the equipment you need

and why you need it A diagram of the set up of your experiment Which variable(s) you will change and which

you will keep the same Which measurements you would need to

make to test your hypothesis State the number and range of

measurements and how you will use them to test your hypothesis

What needs be included in your plan?

A list of risks that are linked to your experiment and how each risk can be reduced to make your experiment safer.

What needs be included in your plan?(Cont….)

Part A - Planning

• State the hypothesis you will be investigating

• Explain your hypothesis using scientific ideas (explain why do you think what you have predicted will happen)

Part A – Planning

Control Variables• List all the variables you will control and

explain how you will control them• Explain why is it necessary to control the

variables that you have listed

Part A – Planning

Risks

• Write down any potential risks that you will need to consider and explain what would you do to reduce these risks.

Part A – Planning

Important• You will need to write a detailed method on how

you will test you hypothesis (carry out your investigation)

• Include all the measurements you will make• Include the range of measurements you will

make and explain why this range was chosen (e.g. increasing the voltage makes bulb brighter, so increasing the intensity of light falling on the LDR will change its resistance (decrease))

Overall Plan

• What calculations you will carry out• What graph will you draw• Explain how your investigation will test

your hypothesis, e.g. 1. vary brightness of bulb (how?)2. record current and resistance (using?) for

different intensities of brightness3. This will allow me test my hypothesis

because…..

Overall Plan (cont)

Part B - Observations

• Results table with correct headings including units and columns for repeated results.

• Make sure you have recorded the current in Amps and the resistance of the LDR in Ohms.

• Secondary Evidence from another pupil needs to copied.

• You will need to comment on the credibility of the secondary evidence, e.g. how do you know the secondary evidence is reliable and valid

Part C - Processing Evidence

• You must include calculate the mean values for your resistance readings accurately to an appropriate number of decimal places.

• You must draw a line graph (resistance of LDR against current in the bulb) using a suitable scale. Label axis with quantity and units

• Draw line of best fit (straight line or curve)

Quality of Evidence

• You must comment on the quality of your own results (primary evidence), identify any anomalous results or state there isn't any

• You must explain why all results are included ( all follow the same trend, very close to each other) or some are excluded (e.g. when you calculated means or when line of best fit is drawn)

• You must make a relevant comment about the quality of the secondary evidence (you may need to draw a graph for secondary evidence to justify your comment)

• You must take account of anomalies when processing your data (included all results when means calculated or not? explain)

• Compare primary and secondary evidence

Quality of Evidence - cont.

Conclusions based on evidence• You must write a conclusion based on

your collected evidence, e.g. as the light intensity (or brightness) of the bulb increased the resistance (measured by the ohmmeter) of the LDR decreased or vice versa

• Important to use your graph to reinforce the relationship between the resistance and the current to show that the resistance of the LDR is affected by brightness of the bulb (brightness linked to current)

• You need to link this conclusion back to your hypothesis (is this what you predicted? You need to comment on this)

• You need to explain your conclusion using scientific ideas, discuss how well the LDR conducts electricity when its placed in darkness/brightness, number of electrons flowing per second? Why this changes in different light intensities

Conclusions based on evidence – cont.

Evaluation of conclusion

• You need to evaluate the conclusion based on your evidence and relevant scientific ideas e.g. write down what your evidence shows (dimmer the bulb the higher the resistance measured on the ohmmeter). The higher the resistance of the LDR means less current is flowing through the LDR

• Suggest how the results you have recorded could be improved and extended and how this will provide stronger support for your conclusion.

(wider range of current readings, so more variation in the brightness of light.

More current readings, with smaller intervals between readings.

Use different LDR’s to see if the same relationship between resistance and brightness exists.)

Evaluation of conclusion

Evaluation of Method

• You need to describe 2 strengths and 2 weaknesses in the method and relate them to the hypothesis.

• You need to suggest how the method could be improved and how this improves the quality of the evidence collected and relate this to the hypothesis.