# Physics potential divider doubt

## Recommended Posts Hey guys can you please explain to me ( a Physics SL student) how one gets the potential divider formula in terms of R2 and R1. Please show me a step-by-step derivation of the formulas,(I really appreciate it!) Thanks SO much!

Note: In the wiki formula replace VL with V out and Vs with VIn]

##### Share on other sites Correction: Vout=Vin*R2/R1+R2

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I am not a Physics student, but this might help you: http://en.wikipedia.org/wiki/Voltage_divider#General_case

##### Share on other sites Hey! thanks, sadly though I can't grasp what they've written there, appreciate it though

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The whole thing is messing with Ohm's law which is V=IR.

Vout=[r2/(r1+r2)]*Vin

Vin=I(r1+r2) according to Ohm's law. Both resistors are including because Vin is in circuit with both of them.

Vout=Ir2 also according to Ohm's law, only resistor 2 is used by resistor one is between the two voltage areas and the electrons aren't travelling backwards to the first resistor Also according to Ohm's law, I=V/R by rearranging it.

For the whole circuit that'd be I=Vin/(r1+r2) which is just V/total resistance.

You have these equations now and you're trying to get the derivation of Vout which we said was Vout=Ir2 but now we have something to plug in for I Vout=[Vin/(r1+r2)]*r2

This looks way better if you right it down with the division bars This doesn't look the exact same as the formula you posted but since it's fractions you can literally move the denominator under the r2 and it's the same thing (yay multiplication) and that is what you posted.

This is all that wiki page was saying, but it was using some different letters and such.

SL Electricity revolves around Ohm's law and the P=IV, if you master those two (and the silly emf equation) and be able to manipulate them to no end, you'll be fine Edited by Drake Glau
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##### Share on other sites Thanks Drake for the advice, I'll master those equations, no doubt. But there's a sum in textbook that requires me to change the subject to R1 So as to get its value.  ##### Share on other sites

Thanks Drake for the advice, I'll master those equations, no doubt. But there's a sum in textbook that requires me to change the subject to R1 So as to get its value.  If you're required to calculate R1, then you will be given the other required values, and you will simple need to manipulate and solve using algebra right? Or is it something else you are stuck on?

##### Share on other sites Thanks Drake for the advice, I'll master those equations, no doubt. But there's a sum in textbook that requires me to change the subject to R1 So as to get its value.  If you're required to calculate R1, then you will be given the other required values, and you will simple need to manipulate and solve using algebra right? Or is it something else you are stuck on?

No its was the manipulation, but it was tough, not Studies SL level! haha!

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