Difference between (R) electrical resistance and (r) Internal resistance??

[pineappletree]

For the equation of
I=(emf)/(R+r)

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[BerkReviewTeach]

For the equation of
I=(emf)/(R+r)

V = IR is the root of this relationship, where the voltage source is a chemical battery. The voltage is the emf of the battery. The total resistance of the circuit includes the resistance of the wire and circuit elements (R) and the internal resistance of the battery itself, which they are calling r. The total resistance is that of the battery and the circuit, r + R. So V = IR becomes emf = I(R + r), making I = emf/(R + r).

This question looks really familiar, but I can't place whether it's from a BR book or practice exam. Where are you coming across this, because it mught help to discuss it in context?

 

[PiBond]

internal resistance (r) is a result of an intrinsic resistance of the battery. thus the Voltage of the batter is equal to the emf minus the Ir. Emf is sometimes referred to as the pure voltage of the battery. the other resistances in a circuit are generally denoted R (include resistors and such) and are added to the internal resistance to determine the current drawn from the battery

 

[pineappletree]

Thank you!! That is perfect


But I was wondering,
what is the point of a resistor?? (I don't understand...)
Why not just use a battery with a lower emf??
Does the resistor perhaps create the emf in the battery via voltage potential??

 

[lorenzomicron]

Thank you!! That is perfect


But I was wondering,
what is the point of a resistor?? (I don't understand...)
Why not just use a battery with a lower emf??
Does the resistor perhaps create the emf in the battery via voltage potential??

if the two terminals of the battery are connected with a wire, which, lets just say has no resistance at all (this is impossible), then the current would be "infinite"- i.e. a short circuit which would destroy the battery. also, resistors and other circuit elements allow voltage to be harvested for work.

 

[BerkReviewTeach]

But I was wondering,
what is the point of a resistor??

Your computer, refrigerator, light bulb, etc... are all resistors. They drain power (energy over time) from the circuit and in doing so slow the current down.