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AQA Physics Specimen Paper 1 (A-level) Question3

Capture3.PNGWill someone help me to make sense of the answers to question 3.2 please?
Reply 1
Avatar for Ladkus
Ladkus
12
Look at the circuit as 2 separate circuits. If the resistance of R1 is 0 ohms what does the voltage need to be across R3 (apply Kirchoff's 2nd law)
Original post by Ladkus
Look at the circuit as 2 separate circuits. If the resistance of R1 is 0 ohms what does the voltage need to be across R3 (apply Kirchoff's 2nd law)


What about the other circuit then? 12Vs and R2 only get 2? How does that work?
Reply 3
Avatar for Ladkus
Ladkus
12
Yes R2 only gets 2 volts. Since the resistor R3 is in parrallel with both V1 and V2 then the potential difference across R3 must be the same for each circuit. If you look at the left circuit on its own the potential difference across R3 must be 10 volts so looking at the right circuit R2 must have 2 volts across it as 12 - 10 = 2

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