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# Help with a 1 mark as level electricity question? Watch

2. (Original post by Jas1947)
You need to break it down into simpler chunks.

we know the PD across RA and RB is the same because they are in parallel with each other.
and the resistance of RB is 2x the resistance of RA so the current in RB must be some proportion of the current in RA because I=V/R
and we know power is given by P=IV
so we know the power dissipation of RB as a proportion of the power dissipated in RA

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Now the current in RC will be equal to the sum of the currents in RA and RB
so we can find the power dissipation in RC using the rule P=I2R

then we just need to add the 3 power dissipations together to get the total being supplied by the battery.

Updated: October 17, 2016
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