Question

PRACTICAL 2. You are provided with a rheostat, an ammeter, a voltmeter, a 1Ω standard resistor, a key, a source of electricity of emf E and connecting wires. (i) Use the electrical components provided to connect the circuit as shown in the diagram, leaving the circuit open. (ii) Connect the voltmeter to the terminals of the battery and record the voltmeter reading, V_T. (iii) Close the key and adjust the rheostat so that the ammeter reads I=0.3A. Record the corresponding voltmeter reading V. (iv) Evaluate I⁻¹ and G=1/I. (v) Repeat the experiment for four other values of I=0.5A, 0.7A, 0.9A and 1.1A. In each case, record the corresponding value of V and evaluate I⁻¹ and G. (vi) Tabulate the results. (vii) Plot a graph with I⁻¹ on the vertical axis and G on the horizontal axis. (viii) Determine the slope, s, of the graph. (ix) Using the graph, determine the value of V for G=2.5. (x) State two precautions taken to ensure good results.

Accepted Answer

This experiment investigates the relationship between current and the internal resistance/emf of the circuit using the given rheostat-ammeter-voltmeter setup. For each set current I (0.3A to 1.1A), the corresponding voltmeter reading V is recorded, and I⁻¹ and G=1/I are computed. Plotting I⁻¹ against G produces a straight line, and its slope gives information related to the emf/internal resistance of the source. From the sample data and graph: slope s=(3.45-1.5)/(3.5-0.975)VA⁻¹=0.772V·A⁻¹. From the graph, when G=2.5VA⁻¹, I⁻¹=2.7A⁻¹. Since G=V/I, V=G×I=G÷I⁻¹=2.5VA⁻¹/2.7A⁻¹≈0.926V.
Precautions: ensure tight electrical connections throughout the circuit; avoid parallax error when taking readings on the ammeter/voltmeter.

WAEC Physics 2023 Theory — Question 14

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