Alternative A
Question 3A
You are provided with an accumulator, an ammeter, a 2ῼ resistor, a key, K, a resistance wire BP, a crocodile clip, J and other necessary materials.
- Connect the circuit as shown in the diagram above.
- Use the crocodile clip to hold the resistance wire at D such that BD = d = 80 cm.
- Close the key, read and record the ammeter reading, I. evaluate I-1.
- Repeat the procedure for four other values of d = 70 cm, 50 cm, 40 cm, and 30 cm. in each case, record I and evaluate I-1
- Tabulate the results.
- Plot a graph with d on the vertical axis and I-1 on the horizontal axis. Determine the slope, s, the graph.
- State two precautions taken to ensure accurate results.
(b) (i) State two factors on which the sensitivity of a moving-coil galvanometer depends.
(ii) A resistance wire of diameter 0.6cm has a resistivity of 1.0 x 10-6ῼ m. What length of the wire would be needed to make a 4 ῼ resistor?
Observation
Part (a) Performance was fair. This was another popular question and it was attempted by majority of the candidate. However, few of the candidates could not chose convenient scales because of the decimal numbers involved.
Part (b) Candidates responded unsatisfactorily.
The expected response:
3. (a) OBSERVATIONS
(i) Five values of d correctly measured and recorded to at least 1 d.p in cm
(ii) Five values of I correctly read and recorded to at least 1 d,p in A and in trend.
Trend: As d decreases, I increases.
(iii) Five values of I -1 correctly evaluated to at least 3 d.p
(iv) Composite table showing at least d, I and I – 1.
GRAPH
(i) Both axes correctly distinguished
(ii) Reasonable scales
(iii) Five points correctly plotted
(iv) Line of best fit.
SLOPE
(i) Large right – angled triangle
(ii) ∆ d correctly determined
(iii) ∆ I-1 correctly determined
(iv) correctly evaluated
PRECAUTIONS
- Ensured clean terminals.
- Ensured tight terminals/connection.
- Opened key when reading was not taken.
- Avoided parallax error on ammeter.
- Avoided sliding crocodile clip on resistance wire.
- Zero error noted/corrected/avoided on ammeter.
- Repeated readings shown in table.
b (i) Factors on which the sensitivity of moving coil galvanometer depends.
- Number of turns of coil.
- Area of coil.
- Strength/intensity of magnetic field.
- Weak hair spring.
(ii) (1)
= (½) OR L
= 113.04 m[½]