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GCSE Physics Question

So I was convinced I had got this question right on my mocks, but my teacher said I did it wrong and won't tell me how to redo it. I got 7A as the answer??

The battery powers 4 motors in the drone. Each motor has a resistance of 1.6 Ohms when the power input is 19.6W. The 4 motors are connected in parallel with the battery. Calculate the current in the battery.
Reply 1
Original post by mamasaywhatnow
So I was convinced I had got this question right on my mocks, but my teacher said I did it wrong and won't tell me how to redo it. I got 7A as the answer??

The battery powers 4 motors in the drone. Each motor has a resistance of 1.6 Ohms when the power input is 19.6W. The 4 motors are connected in parallel with the battery. Calculate the current in the battery.


I got 3.5 amps
Reply 2
Not sure if i'm right but i got 1.75 amps

edit: above answer is correct i think, i worked it out as if it was series rather than parallel
(edited 6 years ago)
Reply 3
Original post by mamasaywhatnow
So I was convinced I had got this question right on my mocks, but my teacher said I did it wrong and won't tell me how to redo it. I got 7A as the answer??

The battery powers 4 motors in the drone. Each motor has a resistance of 1.6 Ohms when the power input is 19.6W. The 4 motors are connected in parallel with the battery. Calculate the current in the battery.


Answer is 1.75 amps I meant
Reply 4
Original post by ray44
Not sure if i'm right but i got 1.75 amps

edit: above answer is correct i think, i worked it out as if it was series rather than parallel


It’s either 3.5 or 1.75 I’m not surw
It will be 1.75 because total current is 3.5A. In parallel current 1 + current 2=current total
Original post by Mitchchambo
It will be 1.75 because total current is 3.5A. In parallel current 1 + current 2=current total


How did you work that out? Because I tried to find the total resistance first which is 1/Rt = 1/R1 +1/R2 +1/R3 +1/R4
Reply 7
Original post by mamasaywhatnow
How did you work that out? Because I tried to find the total resistance first which is 1/Rt = 1/R1 +1/R2 +1/R3 +1/R4

Use the formulae v=isquaredr
Rearrange to get I
Reply 8
Original post by Skkkk
Use the formulae v=isquaredr
Rearrange to get i

Isnt the parallel equation p=v2÷r for dissipation in parallel
P = I^R
I = square root of P/R
The current of each resistor is the square root of 19.6/1.6
Which is 3.5
The current in a circuit splits off and the total current going in is the total going out so the total current is 3.5×4 which is 14
I think this is right, I got your answer at first but I think the reason it is wrong is because if you work out the total resistance then you're assuming that the power is not the same everywhere in the circuit when I think it is if you get me. I'm an A level physics student so this should be easy to me lol. 90% sure this is wrong

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