HEEELLPPPPPP physics Isaac Physics internal resistance

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anonymouspersona
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#1
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#1
An identical cell is placed both in parallel with the first cell and in parallel with the resistor of resistance R, which are already in parallel with each other. The total power dissipated in the circuit is now P2. The ratio P2/P1=7/5
What is the ratio R/r? 2sf
help please I have no idea how to even start this
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amlen
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#2
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Hi, this is eight months later sorry

if you start with finding the total resistance in both circuits in terms of r and R and putting them into the equation P=v^2 / R(total)
this will give you the power dissipated in the whole circuit.

power of the first circuit will be equal to p1=( v^2 )/ (R+r)

and for p2= ( v^2 )/ (r/2 + R)

the value for P2/P1 = 7/5
so if you substitute those equations into that ^^ and rearrange until you get to R/r

you should get your answer

if that makes sense? sorry if it doesn't
(the reason the total resistance of the second circuit is r/2 + R rather than 2r is because the resistors are in parallel to each other)
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ryanrobsonTV
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#3
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The answer is 0.75
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Callicious
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#4
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#4
(Original post by ryanrobsonTV)
The answer is 0.75
It's against the forum guidelines to give out answers (true or false- I didn't check if the answer is.)
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