Alternative B
Question 3B
You are provided with a battery, an ammeter, a voltmeter, a resistance box, a key and connecting wires.
- Set up the circuit as shown in the diagram above.
- With the key opened, measure and record the e.m.f EO of the battery.
- With the key closed, select the resistance R = 1 ῼ on the resistance box. Read and record the current, I.
- Evaluate I-1.
- Repeat the procedure for five other values of R = 2 ῼ, 3ῼ, 4ῼ, 5 ῼ , and 6ῼ.
In each case, record I and evaluate I-1.
- Tabulate the results.
- Plot a graph with R n the vertical axis and I-1 on the horizontal axis.
- Determine the slope, s, of the graph,.
- State two precautions taken to ensure accurate results.
(b) (i) Define potential difference in an electric field.
(ii) A piece of resistance wire of diameter 0.2 mm and length 25 cm has a resistance of 7 ῼ.
Calculate the resistivity of the wire. {
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Observation
Part (a) Candidates performance was fair. Many candidates attempted this question and the response was fair.
Part (b) Candidates response was satisfactory.
The expected response:
3 (a) OBSERVATIONS
- Eo correctly measured and recorded to at least 1 d.p in volts.
- Six values of R correctly recorded in Ω.
- Six values of I correctly read and recorded to at least 1 d.p in A and in trend.
Trend: As R increases, I decreases.
- Six values of I-1 correctly evaluated to at least 3 d.p
- Composite table showing at least R, I and I-1.
GRAPH
- Both axes correctly distinguished
- Reasonable scales
- Six points correctly plotted
- Line of best fit.
SLOPE
- Large right – angled triangle
correctly determined - ∆ I-1 correctly determined
correctly evaluated
INTERCEPT
Intercept C on the vertical axis
Correctly shown
Correctly read
ACCURACY
Based on slope, s, = Eo ± 10 %
PRECAUTIONS
- Ensured clean terminals.
- Ensured tight terminals/connections.
- Opened key when reading was not taken.
- Avoided parallax error on ammeter.
- Zero error noted/corrected/avoided on ammeter.
- Repeated readings shown on table.
b. (i) Potential Difference in an electric field
It is the work done per coulomb in moving a charge between two points.
O R
It is the energy per coulomb released when electricity moves from one point to the other.
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(ii) ρ
= = 8.8x10-7