Physics

Problem

A lamp and a resistor

R = 10\,\Omega

are connected in series to a variable DC supply. The current

I

through the circuit is measured for different supply voltages

V_{\text{s}}

. The following data are obtained: a. (i) Using the readings in the table, calculate the potential difference

V_{\text{R}}

across the resistor for each supply voltage.

V_{\text{s}}

(V): 3, 6, 9, 12

I

(A): 0.20, 0.35, 0.45, 0.50 b. (ii) Hence determine the potential difference

V_{\text{lamp}}

across the lamp for each case. c. (iii) Plot (qualitatively) the

V_{\text{lamp}}

–

I

graph for the lamp and state whether the lamp obeys Ohm’s law, giving a reason. d. (iv) Discuss how the presence of the ohmic resistor in series influences the overall shape of the circuit’s

V

–

I

characteristic at low and at high supply voltages.

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