A student constructs the schematic circuit described below
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A student constructs the schematic circuit described below.
• A battery of emf 12V and negligible internal resistance is connected to a single-pole single-throw switch.
• Beyond the switch, the circuit branches into two parallel paths:
– Path A contains only a resistor R1=100Ω.
– Path B contains a light-activated switch (open in darkness, closed when illuminated) in series with a resistor R2=50Ω and a capacitor of capacitance 10μF.
• The two paths recombine and return to the negative terminal of the battery.
A schematic voltmeter symbol is connected so that its leads make contact at two nodes labelled X and Y on Path A, straddling R1. An ammeter symbol is inserted somewhere in the circuit, but its exact placement is not specified.
Answer the following questions.
(1) Determine a placement for the ammeter that will allow an accurate reading of the total current supplied by the battery regardless of the state (open or closed) of the light-activated switch. Explain your reasoning in terms of current distribution in the branches.
(2) Assume the light-activated switch is open (dark conditions). Describe qualitatively the reading you would expect on the voltmeter and on the ammeter you placed in part (a). Justify your answer without performing explicit numerical calculations.
(3) When the circuit is suddenly illuminated, the light-activated switch closes. Describe the immediate effect on the ammeter reading and on the voltmeter reading. Then, explain how each reading evolves over time until a new steady state is reached, considering the presence of the capacitor.