Uses of Magnetism (OCR Gateway GCSE Physics)

Topic Questions

1a3 marks
i)
Name the rule which can be used to predict the direction of the force perpendicular to a current-carrying conductor in a magnetic field.

[1]

ii)

A student places four wires of different lengths (A, B, C and D) perpendicular to different magnetic fields with different currents flowing.

Look at the table of the results.

Wire Magnetic fluxdensity (T) Current (A) Length (m)
A 0.10 2.5 0.50
B 0.15 2.0 0.75
C 0.20 4.5 0.25
D 0.25 5.0 1.00


Use the results to show that wire D experiences the highest force.

Show your working.

[2]

1b6 marks
i)
The student decides to build a model transformer.

The transformer is a step-up transformer which doubles the input voltage.

Describe how she could build this step-up transformer in a science laboratory.

[4]

ii)
Suggest one risk associated with this experiment and how it can be reduced.

[2]

1c2 marks

Describe how a microphone works.

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2a3 marks

The diagram below shows the structure of a transformer.

q23-paper4-specimen-ocr-gcse-physics

The alternating current in the secondary coil is greater than in the primary coil.

Explain why.

2b2 marks

The secondary coil produces an output of 12 V.

Calculate the number of turns in the secondary coil.

Show your working.

2c4 marks

A transformer is used to increase voltage from 25 000 V up to 400 000V before transmission through the National Grid. Therefore, the voltage increases by 16 times.

i)
Explain how this increase in voltage would affect the current, assuming that the power remains constant.

[2]

ii)

     The formula to work out power is:

   power = current2 × resistance

Explain, using a calculation, why this increase in voltage is important to power loss in transmission cables.

[2]

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