O-LevelPhysicsMagnetism5054/21 · May/June 2018 · Q85 Marks

Fig. 8.1 shows a transformer connecting an overhead 25000 V electrical power line to a house. [Figure 8.1]

(a)State whether coil A or coil B in the transformer has the larger number of turns. Give a reason for your answer.[1]
(b)One purpose of using an iron core in the transformer is to increase the magnetic field inside coil A. State one other purpose of using the iron core.[1]
(c)Describe briefly how an output voltage is induced in coil B.[1]
(d)Suggest one advantage and one disadvantage of burying a power line underground rather than having an overhead power line. advantage disadvantage[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[B1] coil A (has more turns) and voltage to house less than 25 000 V / step down transformer
[B1] to transfer the field from primary to secondary or to increase flux / field / flux linkage in coil B
[B1] changing magnetic field / flux (in B or secondary) or field lines cut
[B1] advantage: • visual effect • ability for more development above ground • no chance of touching it and electrocution (in normal use) • less likely to be damaged by storm / wind
[B1] disadvantage: • cost of construction • difficulty of maintenance or damage due to digging / erosion • difficulty of knowing where line is / finding or repairing faults

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.