Part (a). This question attracted many candidates and their performance was above average.
Part(b) This was another popular question. In the first part; performance was low while in the second
part performance was above average.
Part(c) This was also popular among the candidates and the performance was above average. However,
some diagrams are not workable. Their diagrams either has the gold leaf or earthting omitted.
Part(d) (i) This was not a popular question among the candidates. Candidates were evidently unfamiliar
with the device. Teachers should teach electromagnetic induction fully. Performance was
low.
(ii) The performance of candidates was above average in this part as majority of the responding candidates were able to list correctly the two factors.
- Many candidates were unable to state the correct formula. Hence substitution and arithmetic calculation was affected performance was low.
The expected answers are:
11. (a) Electromotive force emf
The emf of a cell is the energy needed to take a unit positive charge round a circuit in
which the cell is connected.
The p.d across the terminals of the cell when the cell/battery/generator is on open circuit
The energy per unit charge transformed in the cell.
(b)(i) Principle of operation of a Potentiometer
The p.d across the wire is (directly) proportional to the length of the wire OR
When a steady current flows through a uniform wire, equal
lengths of the wire will have equal potential difference
(Accept V L where V and L are correctly specified).
(ii) Advantages of Potentiometer over Voltmeter
e.g - It is more accurate.
It is more sensitive
It eliminates error due to internal resistance of the cell
(c)(i) Labelled sketch of Gold Leaf Electroscope
(ii) Uses of Gold-leaf Electroscope
e.g To:
- detect electrostatic charge
- detect the nature of electrostatic charge
- determine the magnitude of the induced charges.
(d)(i) Magnetic Relay
The mode of action of magnetic relay relies on the principle of electromagnetic induction .
A small current passing through one circuit controls another circuit containing devices which
requires larger current
(ii) Factors affecting induced emf in a coil
e.g the - speed of rotation of the coil
- magnetic field strength
- cross-sectional area of the coil
- number of turns in the coil
(iii) F = IBLsin
OR
Force per unit length = = IB sin
= 5 x 2.0 x 10-3x sin30°
= 5.0 x 10-3 Nm-1
