# 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!
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!

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,