Question 11
(a) State Lenz’s law.
(b) State two applications of magnets.
(c)
The diagram above illustrates a step-down transformer.
(i) State a reason for using:
(α) two coils;
(β) an iron core;
(ɣ) an alternating supply.
(d) 
A circuit is connected as shown above. If the resistance of the voltmeter is 200, calculate the voltmeter reading.
Observation
Part (a): Candidates performance was fair. Majority of the candidates were unable to correctly state Lenz’s law but rather were Faraday’s experiment.
Part (b): Candidates performance was good.
Part (c) Performance was poor.
Part (d): Performance was fair. Most candidates were able to define resistivity but failed to add additional information like the unit of resistivity to score full mark.
Part (e): Performance was poor. Few candidates were able to score full mark. Most candidates were able to solve the problem.
The expected answer is:
11.(a) Lenz’s Law
Lenz’s law states that the direction of an induced emf/current is always such as to oppose the change producing it
(b) Applications of Magnets
e.g used in
- electric motors/generators;
- electric bells;
- sorting out magnetic from non-magnetic materials;
- cranes;
- refrigerator door;
- magnetic compass.
(c)(i)(α) Reasonfor Using two coils
Two coils are used to vary input and output voltages/currents
(β) Reason for Using an Iron Core
Iron core is used for effective magnetic flux linkage
(ɣ) Reason for Using an Alternating supply
Alternating supply is used to produce changing magnetic flux
