The Student Room Group

How do i find the EMF?

A voltmeter with a resistance of 20 kilo ohms connected across a power supply gives a reading of 44V. A voltmeter with a resistance of 50 kilo ohne connected across the same power supply gives a reading of 50V. What is the EMF of the power supply.? I’m unsure of what to do here
emf = IR + Ir
emf = V + Ir
I=V/R=44/20000=2.2*10^-3 A
I = V/R=50/50000=1*10^-3 A
V + Ir = V + Ir
44 + 2.2*10^-3 r = 50 + 1*10^-3 r
1.2*10^-3 r = 6
r = 5000 ohms
emf = V + Ir
emf = 44 + (2.2*10^-3) * 5000 = 55 V
Hope that helps!:smile:
Original post by Terry Li
emf = IR + Ir
emf = V + Ir
I=V/R=44/20000=2.2*10^-3 A
I = V/R=50/50000=1*10^-3 A
V + Ir = V + Ir
44 + 2.2*10^-3 r = 50 + 1*10^-3 r
1.2*10^-3 r = 6
r = 5000 ohms
emf = V + Ir
emf = 44 + (2.2*10^-3) * 5000 = 55 V
Hope that helps!:smile:


Hi Terry, thanks for helping OP.
It would be better that you guide OP in getting answers and explain the physics concept(s) behind it instead of doing all the work for OP.

I believe the following:
We cannot learn physics by seeing others “doing” the physics problems.
We learn physics by solving physics problems ourselves.

Thanks,

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