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# AS Physics question: wts the diff. between EMF and PD? watch

1. what is the difference between electromotive force and potential difference?
I read thos revision guide and text book but still don't understand what it means.., can someone help please
2. Potential difference is transferring electrical energy into other forms (heat, light, sound). EMF is transferring other forms of energy into electrical (eg. chemical energy stored in a battery).
3. EMF is a gain in energy per unit charge
PD is a Loss in energy per unti charge
4. (Original post by Nylex)
Potential difference is transferring electrical energy into other forms (heat, light, sound). EMF is transferring other forms of energy into electrical (eg. chemical energy stored in a battery).
I dont think this is correct?
5. So due to conservation of energy, EMF = PD?
6. As far as the AS exam is concerned, just assume that they are the same.

EMF is what drives current. PD is the potential energy per unit charge.
7. So the difference between them is the energy lost in the circuit?
8. EMF is the voltage supplied by an active component (battery, dynamo, etc). PD is the voltage accross a passive component (resistor, capacitor, etc).
9. So can you say the PD across a battery with EMF 5V is 5V?
10. (Original post by mik1a)
So can you say the PD across a battery with EMF 5V is 5V?
if you disregard internal resistence (i.e. the current through the battery is 0A), yes.
11. (Original post by imasillynarb)
I dont think this is correct?
Well then you're a silly narb!

EMF is the amount of energy stored in the battery converted to electrical energy per unit charge passing through the battery.

P.D. is the amount of electrical energy per unit of charge converted to other forms of energy in while passing through a component.
12. So the difference between the two is equal to the internal resistance?
13. (Original post by mik1a)
So the difference between the two is equal to the internal resistance?

Not equall to, but determined by.
14. Not equal to?
15. (Original post by mik1a)
Not equal to?

Here's an example:

EMF of battery: 5V

Internal resistance: 0.5ohms

Current: 2A

Then the voltage lost through internal resistance (V= IR) = 1V

So if you have a component on the circuit, pd = 4V

I think
16. (Original post by hitchhiker_13)
Here's an example:

EMF of battery: 5V

Internal resistance: 0.5ohms

Current: 2A

Then the voltage lost through internal resistance (V= IR) = 1V

So if you have a component on the circuit, pd = 4V

I think
Ok thankyou very much, I never understood internal resistance. Now I have an idea at least.
17. (Original post by mik1a)
Ok thankyou very much, I never understood internal resistance. Now I have an idea at least.

Well, glad to help, but if your physics teacher tells you otherwise I would take their word for it!

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