Question

3. Connect the circuit as shown (battery, key, rheostat, ammeter and voltmeter with resistors R₁ and R₂) leaving the key open. Close the key and adjust the rheostat until the ammeter reads I = 0.20 A. Record the corresponding voltmeter reading, V. Repeat the experiment for I = 0.30 A, 0.40 A, 0.50 A and 0.60 A, recording V, Log V and Log I for each case. Tabulate the results, plot a graph of Log V on the vertical axis against Log I on the horizontal axis (starting both axes from the origin), determine the slope, s, of the graph and the intercept, c, on the Log V axis, and calculate the value of R in the equation Log RT = c. State two precautions taken to obtain accurate results.

Accepted Answer

Sample results: I(A): 0.20, 0.30, 0.40, 0.50, 0.60; V(V): 0.13, 0.20, 0.27, 0.34, 0.40; log I: −0.70, −0.52, −0.40, −0.30, −0.22; log V: −0.90, −0.70, −0.60, −0.50, −0.40.
Slope, s = ΔlogV/ΔlogI = (−0.28−(−0.70))/(−0.1−(−0.5)) = 0.42/0.4 ≈ 1.04.
Intercept on the log I axis ≈ 0.17. Since log RT = c, RT = 10^0.17 ≈ 1.48 Ω.
Precautions: ensured tight connections of the wires, key and other component parts of the circuit; avoided errors due to parallax when taking readings on the ammeter and voltmeter.

WAEC Physics 2025 Theory — Question 34

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