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# AS Physics help - circuits watch

1. Hi, I’m not sure how to do this question because there’s both series and parallel parts and I don’t know how to split the voltage and current, if anyone could help me I’d be grateful!
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A resistor of 85Ω is in series with a parallel arrangement of 60Ω and 20Ω, and a p.d of 120V is connected across the whole circuit. Calculate (a) the current in each resistor, (b) the p.d across each resistor
2. The first thing you should do is draw the circuit out, this will help you better visualise the problem.

For the first problem, use Kirchoff's First Law's implication, that the current in a series circuit is constant.

Now, to find the Total Resistance, do the 1/(1/60 + 1/15), to find the resistance of the parallel arrangement, add that on to the resistor in series for total resistance.

V = IR, you can now find the current in the series circuit.

For the first problem, you should be able to recall that Currents in the parallel arrangement should sum up, and you know the total current of the whole series arrangement, so you can split the resistors as ratios in order to divide the total current.

For the PD, well you know the Currents, and you know the Resistances, so go ahead.
3. (Original post by AryanGh)
The first thing you should do is draw the circuit out, this will help you better visualise the problem.

For the first problem, use Kirchoff's First Law's implication, that the current in a series circuit is constant.

Now, to find the Total Resistance, do the 1/(1/60 + 1/15), to find the resistance of the parallel arrangement, add that on to the resistor in series for total resistance.

V = IR, you can now find the current in the series circuit.

For the first problem, you should be able to recall that Currents in the parallel arrangement should sum up, and you know the total current of the whole series arrangement, so you can split the resistors as ratios in order to divide the total current.

For the PD, well you know the Currents, and you know the Resistances, so go ahead.
Ahh right that makes sense to me now, thank you!!

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