You will complete 12 Specified Practical Activities if you are studying GCSE Physics. You could be asked questions about the apparatus, methods, safety precautions, results, analysis and evaluation of these experiments.
A student investigates the relationship between the number of turns of coil on an electromagnet and its strength. The diagram shows how the experiment was set up.
The student started off by having a 10 turn coil, switched it on and counted the number of paper clips that stuck to it. Here are the results.
|Number of turns||Number of clips|
a) Use some graph paper to draw a graph of the result, with the number of turns on the x-axis. [3 marks]
b) Another student predicts that a 60 turn coil would hold 30 clips. Do you agree or disagree with this? Give a reason for your choice. [2 marks]
c) A second investigation was attempted to try and find the relationship between the current through the coil of an electromagnet and its strength. Outline briefly how this could be done listing any extra apparatus that is needed. [4 marks]
a) Graph that starts off straight but gradually curves with a decreasing gradient.
b) Disagree. The graph is not straight and not proportional . Trebling the number of coils will not treble the number of clips .
c) Two extra items of apparatus would be needed, an ammeter and a variable resistor . Fix the number of turns, say 30, for the whole investigation . Increase the current in steps using the variable resistor and count the number of clips that stick each time . Record the results as above, but the first column heading would be current then plot a graph of the results .
a) State how the construction of a step-up transformer is different from a step-down transformer. [1 mark]
The above diagram shows a transformer that can be used for an investigation in a laboratory.
b) Explain why there must be an alternating input voltage for the transformer to work. [2 marks]
c) An investigation is carried out to determine how the output voltage depends on the number of turns on the secondary coil. The input voltage (8 V) and the number of turns on the primary coil (200) are kept constant throughout the investigation.
The results of the investigation are recorded in the table below.
|Input voltage (V)||Primary turns||Secondary turns||Output voltage (V)|
i) What is the value of the missing data? [1 mark]
ii) Use graph paper to plot a graph of the output voltage against the number of secondary turns and draw a suitable line. [3 marks]
iii) Describe the relationship between the output voltage and the number of secondary turns. [2 marks]
iv) Use the graph to find the number of secondary turns required to give an output voltage of 5 V. [1 mark]
v) Explain how the graph would be different if the investigation were repeated with a primary coil containing 400 turns. [2 marks]
a) It has more secondary or output turns or coils than primary turns (or converse). 
b) An ac produces a changing magnetic field  that induces a voltage/current in the secondary or output coil .
c) i) 100 
ii) All plots correct.
Straight line through the points from 50 - 300 turns.
iii) Output voltage increases as number of secondary turns increase  and does so proportionally/uniformly/at a constant rate .
iv) 125 
v) Less steep line/smaller gradient. 
As each output or voltage would be halved.