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# Please can anyone help me with electrical circuit calculations?

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Evening all. Am doing a physics coursework on electrical circuits, calculating resistance, etc and I have done it all except ONE question which I just cannot figure out how to do it (I missed the o… Read More
7y, 1m agoPosted 7 years, 1 month ago
Evening all.

Am doing a physics coursework on electrical circuits, calculating resistance, etc and I have done it all except ONE question which I just cannot figure out how to do it (I missed the one lesson we were maybe taught it in).
I have already filled one A4 page with calculations but am not confident with it at all, please could any of you clever peeps take a look for me - will put the diagram in 2nd post

Would really appreciate any help x x x
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7y, 1m agoPosted 7 years, 1 month ago
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(6)
#1
(a) e.m.f of battery
(b) Current in 20Ω resistor
(c) Power supplied to each of the 4 resistors

:-D:-D:-D

1 Like #2
I don't know what methods are currently taught, but this is how I solve part a.

This can be considered as two circuits with a shared power source, so ignore the first circuit (because we know less about it than the second circuit) and add lables.

V = e.m.f of battery
V1 = voltage across 4 ohm resister
V2 = voltage across 3 ohm resister
The two resistors are in series so the current flowing through them will be the same (1.5 amp).

From ohms law (V = IR):
V1 = 1.5 * 4
V2 = 1.5 * 3

So V = 10.5.

Now you got the voltage of the battery you can do a similar calculation for the first circuit..
1 Like #3
E=I*R
E=1.5A*(4ohm+3ohm)
E=1.5*7
E=10.5
#4
I=V/R
I=10.5V/(8ohm+20ohm)
I=10.5/28
I=0.375Amps
I=375mA
#5
P=IsquareR
For top set:
P=(0.375A*0.375A)*8ohm
P=0.140625*8
P=1.125W

P=(0.375A*0.375A)*20ohm
P=0.140625*20
P=2.8123W

for bottom row use the given 1.5Amp for each resistor value
#6
Excellent, thanks very much - I've got it now :oops:

Will leave you both rep :)