Alternative B
Question 3B
You are provided with an ammeter, a voltmeter, a resistance box, connecting wires, dry cells and other necessary materials.
- Measure and record the length XY of the resistance wire provided.
- Connect the circuit as shown in the diagram above.
- With R = 0Ω, close the key K. Read and record the current, I and the corresponding voltage drop, V across the wire.
- Setting R = 1Ω, close the key. Read and record the current, I and the corresponding voltage drop, V across the wire.
- Repeat the procedure for five other values of R = 5Ω, 10Ω, 20Ω, 40Ω and 60Ω. Tabulate your readings.
- Plot a graph of V on the vertical axis and I on the horizontal axis.
- Determine the slope, s, of the graph.
- State two precautions taken to ensure accurate results.
(b) (i) Mention and state the law on which the experiment in 3(a) is based.
Observation
Part (a) This was a popular question among the candidates. Candidates performance was fair.
(b) Candidates response was fair.
The expected response:
- Five values of R recorded in ohms
- Five values of I recorded to at least 1d.p in A and in trend
- Five values of I-1 correctly evaluated to at least 3 s.f
- Composite table at least R, I and I-1
- Both axes correctly distinguished
- Plot a graph using reasonable scales
- Draw line of best fit
- Determine the slope and intercept of the graph
- Evaluate
- State any two of the following precautions.
e.g.
- Ensured key opened in between readings/when reading were not taken
- Ensured tight connections
- Avoided parallax error when taking reading on ammeter
- Ensured clean terminals
- Repeated readings shown on table
- Noted/Corrected zero error on ammeter
b(i) R = 10 Ω correctly shown on graph
Corresponding value of I-1 correctly read
I correctly evaluated
(ii) Differences between
Shunt |
Multiplier |
- Connected parallel to/across the milliammeter - Has low resistance - Converts milliammeter to an ammeter |
- Connected in series with a milliammeter - Has high resistance - Converts milliammeter to a voltmeter |