Question 3A
You have been provided with a resistance box, a voltmeter, a key, a battery and other necessary materials.
(i) Connect the circuit as shown in the diagram above
(ii) With the key K closed, read and record the voltmeter reading Vo
(iii) Set the resistance R in the resistance box equal to 1Ω.
(iv) Close the key, read and record the potential difference V on the voltmeter.
(v) Evaluate R-1 and V-1
(vi) Repeat the procedure for five other values of R = 2Ω =, 3Ω, 4Ω, 5Ω and 6Ω.
(vii) Tabulate your readings.
(x) Plot a graph with V-1 on the vertical axis and R-1 on the horizontal axis.
(ix) Determine the slope, s, of the graph and the intercept, e, on the vertical axis.
(x) Evaluate e-1
(xi) State two precautions taken to obtain accurate results.
(b) (i) Define potential difference between two point
(ii) Explain why the emf of a cell is greater than the p.d across the cell when it is
supplying current through an external resistance.
Observation
Part (a) . This question was popular among the candidates and performance was satisfactory.
However, some candidates could not evaluate the reciprocal of R and V to the required accuracy. Most candidates did well in plotting the graph, determining the slope and evaluation of intercept. Precautions were well stated. Majority missed the mark for accuracy
Part (b). Majority of the candidates were able to define p.d while they were unable to explain why the emf of a cell is greater than p.d
Candidates are expected to:
Measure and record Value of Vo to at least 1 d.p in volts
Read and record six values of V to at least 1d.p in volts and in trend
Trend:- as R increases, V increases
Evaluate and record six values of 
to at least 3 d.p
- Evaluate and record six values of 
to at least 3.d.p
- Composite table R, V,
, 
- Distinguish both axes
- Plot graph using reasonable scales
- Draw a line of best fit
- Evaluate the slope
- Deduce 
from the intercept C
- State any two of the following precautions.
e.g.
- Ensured clean terminals/tight connection
- Avoided parallax error in reading the voltmeter
Key removed when reading is not being taken
Noted/corrected zero error in reading the voltmeter
Repeated readings shown on the table
b(i) The p.d (in volts) between two points is defined as the work done (in joules) in
moving a charge of one coulomb from one point to the other.
(ii) Emf (E) is the work done across external resistance R and internal resistance r while
p.d (V) is the work done across the external resistance R, only.