You are Here: Home >< Physics

# Electricity watch

1. Why is the Electromotive force always less than the terminal potential difference ? I cant seem to get my head around his concept.
2. (Original post by abdilighter)
Why is the Electromotive force always less than the terminal potential difference ? I cant seem to get my head around his concept.
It's been a while but I'll give it a go:
The reverse holds actually, the battery has an internal resistance which causes the e.m.f to drop so the e.m.f actually exceeds the potential difference.

However, this is not always the case, for a battery being recharged, the terminal potential difference will actually exceed the e.m.f.

A quick google gave a couple of links you might like to look at:
Regarding the internal resistance.
Regarding the recharging battery.
3. (Original post by abdilighter)
Why is the Electromotive force always less than the terminal potential difference ? I cant seem to get my head around his concept.
emf=V+Ir
4. (Original post by abdilighter)
Why is the Electromotive force always less than the terminal potential difference ? I cant seem to get my head around his concept.
TPD = EMF - Lost Volts, so the EMF is always less as it takes into consideration the lost volts which are deducted as it results in energy dissipated as heat etc
5. (Original post by derpz)
TPD = EMF - Lost Volts, so the EMF is always less as it takes into consideration the lost volts which are deducted as it results in energy dissipated as heat etc
Thank you !
6. (Original post by abdilighter)
Why is the Electromotive force always less than the terminal potential difference ? I cant seem to get my head around his concept.
Work has to be done to get the charges to leave the battery, hence some of the energy is lost due to this 'internal resistance'.
7. (Original post by abdilighter)
Why is the Electromotive force always less than the terminal potential difference ? I cant seem to get my head around his concept.
(Original post by joostan)
It's been a while but I'll give it a go:
The battery has an internal resistance which causes the e.m.f to drop.

However, this is not always the case, for a battery being recharged, the terminal potential difference will actually exceed the e.m.f.

A quick google gave a couple of links you might like to look at:
Regarding the internal resistance.
Regarding the recharging battery.
(Original post by thefatone)
emf=V+Ir
(Original post by derpz)
TPD = EMF - Lost Volts, so the EMF is always less as it takes into consideration the lost volts which are deducted as it results in energy dissipated as heat etc
(Original post by abdilighter)
Thank you !
(Original post by Kyx)
Work has to be done to get the charges to leave the battery, hence some of the energy is lost due to this 'internal resistance'.

isn't V = emf - Ir.
So emf is never less than V
8. (Original post by Xenon17)
isn't V = emf - Ir.
So emf is never less than V
Yes.
Emf is always greater.
9. (Original post by Xenon17)
isn't V = emf - Ir.
So emf is never less than V
Yeah, just remember that equation and you should be fine!
10. (Original post by Kyx)
Yes.
Emf is always greater.
(Original post by derpz)
Yeah, just remember that equation and you should be fine!

Yh but

(Original post by abdilighter)
Why is the Electromotive force always less than the terminal potential difference ? I cant seem to get my head around his concept.
thats where the OP has gone wrong
11. (Original post by Xenon17)
isn't V = emf - Ir.
So emf is never less than V
Yes, that's what I said, although I think I misread the question, so my answer makes less sense.
Thanks for this, will edit.
12. (Original post by Xenon17)
Yh but

thats where the OP has gone wrong
Yes
The OP went wrong saying it is less: it is more
13. (Original post by Xenon17)
isn't V = emf - Ir.
So emf is never less than V
just rearranged it..
14. (Original post by thefatone)
just rearranged it..
v = emf - Ir

adding Ir to both sides gives: v + Ir = emf - Ir + Ir

v + Ir = emf

Or

emf = v + Ir

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 6, 2016
Today on TSR

### The most controversial member on TSR?

Who do you think it is...

### Uni strikes! How do they affect you?

Discussions on TSR

• Latest
Poll
Discussions on TSR

• Latest

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE