Question 11
- State two factors that determine the sensitivity of a moving-coil galvanometer
- Define the farad.
- (i) What happens in a series circuit if more bulbs are added in series?
(ii) A laboratory technician wishes to reduce the current passing through a galvanometer to 0.05 of its initial value by means of a resistor. If the internal resistance of the galvanometer is 100 Ω.
(α) how should the resistor be connected?
(β) calculate the resistance of the resistor.
- The current I in a sinusoidal a.c. circuit is given by I = 40 sin 500 лt, where t is the time in seconds. Use the equation to determine the:
- frequency;
- peak value;
- r.m.s. value of the current
Observation
Part (a): Candidates performance was low. Majority of the candidates did not patronize this question.
Part (b): Candidates performance was poor. Most candidates failed to submit the correct definition of Farad.
Part (c) (i) Performance was below average. Very few candidates commented on resistance, current and brightness of bulbs to earn full mark.
(ii) (α) performance was above average. Most candidates recognize from their submission that the resistor should be connected in parallel to the galvanometer.
(β) Performance was below average.
Part (d): Performance was fair. Most candidates were able to make proper deductions and solved the problems correctly.
The expected answer is:
11. (a) Sensitivity of a Galvanometer
- Magnetic field strength (B);
- Number of turns in the coil;
- Area of coil
- Control springs
(b) Farad
The capacitance of a capacitor that acquires a charge of 1 coulomb when a p. d of 1 volt is applied.
(c) (i) Series Circuit
The resistance in the circuit increases, causing reduction in the strength
of current and brightness of the bulbs.
(ii) (α) The resistor should be connected in parallel (with the galvanometer)
