Please can anyone help me with electrical circuit calculations?

Found 26th May 2010
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

6 Comments

Original Poster

(a) e.m.f of battery
(b) Current in 20Ω resistor
(c) Power supplied to each of the 4 resistors

:-D:-D:-D

http://i596.photobucket.com/albums/tt48/mrszerrouk/Untitled-1.jpg

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.

http://i45.tinypic.com/1zz6s29.jpg

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..

E=I*R
E=1.5A*(4ohm+3ohm)
E=1.5*7
E=10.5

I=V/R
I=10.5V/(8ohm+20ohm)
I=10.5/28
I=0.375Amps
I=375mA

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

Original Poster

Excellent, thanks very much - I've got it now :oops:

Will leave you both rep
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