Past Paper Model Answers

Question 1

How do transformers work?

Answer 1

An alternating current in the primary coil has a B-field around it
Soft iron core strengthens field and links both coils
Change in flux linkage due to AC
EMF induced due to Faraday’s Law
Φ and t are the same in both coils, so the ration of turns gives the ration of EMF across both coils

Question 2

Why might a soft iron core be laminated (alternate layers of iron and plastic)

Answer 2

This prevents an EMF from being induced across the whole core
Prevents eddy current formation
reduces waste heat energy production

Question 3

How does a dynamo torch work?

Answer 3

The handle is squeezed, rotating magnet inside coil
Change in flux linkage
EMF induced in coil due to Faraday’s Law
Current created in coil, which powers bulb
Rotating magnet faster, increasing magnetic flux density and increasing number of turns will increase bulb brightness.

Question 4

How does a 200V neon lamp flash when the switch is opened in a 1.5V circuit containing a coil?

Answer 4

When the switch is closed, current flows through the coil, generating a B-field
Switch opens, field drops causing a change in flux linkage
EMF induced due to Faraday’s Law
Since E=ΔNΦ/Δt, the large number of turns in the coil explains why the bulb lights

Question 5

Explain one advantage of using a data logger and light gate to using a stopwatch

Answer 5

It reduces the chance of human error which means recorded data will be more accurate as the data logger reduces % uncertainty

Question 6

Criticise (a set of) results

Answer 6

Inconsistent significant figures
Lack of precision
Lack of repeats
Not enough data collected