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# Physics: Electricity Watch

1. What is Potential Difference?

What is Terminal Potential Difference?

What is the difference between them?

What is internal resistance?

What is E.M.F?

(I HEARD WHEN CURRENT=0, THE TERMINAL P.D. AND EMF ARE EQUAL, WHY?)
2. I think you would be best off going to a website like Physicsandmathstutor and doing some of their exercises on electricity! That would help you answer those quickly!
3. (Original post by Paranoid_Glitch)
snip
Hi! I moved these threads to the Physics forum - you're more likely to get help here
4. (Original post by Fox Corner)
Hi! I moved these threads to the Physics forum - you're more likely to get help here
Thanks can never seem to get it right.
5. Do you know what potential is? Once you do this is all simple.
6. (Original post by morgan8002)
Do you know what potential is? Once you do this is all simple.
Sorry, but no.
7. (Original post by Paranoid_Glitch)
Sorry, but no.
It's usually defined as the change in the potential energy of a unit charge moved from infinitely away to a point. Unit in this case means that the magnitude of the charge is 1.

Have you studied integral calculus?
8. (Original post by morgan8002)
It's usually defined as the change in the potential energy of a unit charge moved from infinitely away to a point. Unit in this case means that the magnitude of the charge is 1.

Have you studied integral calculus?
Are we not allowed to give answers to these kind of questions in the physics forum? I thought this only applied to calculations.
9. (Original post by M0nkey Thunder)
Are we not allowed to give answers to these kind of questions in the physics forum? I thought this only applied to calculations.
We are allowed. Most of them are definitions which can be Googled anyway. The definitions won't make much sense without the necessary background knowledge though so I was just trying to gauge how much the OP knows before giving them. I may as well give a list now, since potential is the main concept that needs to be known. We're allowed to give answers to calculation questions too, but only as a last resort.

1. The difference between the potentials at two points.

2. The potential difference between the terminals(of a cell/battery). It's the actual potential supplied by the battery to the circuit. It's often denoted by r. In a real battery, this is smaller than the emf(when discharging).

3. As above.

4. The resistance within the battery due to the materials of the battery. It decreases the terminal voltage. In many cases it's assumed to be negligible.

5. The potential supplied to electrons as they pass through the cell/battery. It's usually denoted by and called electromotive force.

6. You can work this out using Kirchoff's loop rule(Kirchoff's second law). Imagine the air having infinite resistance. Then you can draw a loop going through the battery, along the wire and around in the air back to the other side of the wire. You then sum the voltage drops and emfs.
You can also use Kirchoff's loop rule in a circuit and derive the equation , then let I tend to 0.
10. (Original post by morgan8002)
We are allowed. Most of them are definitions which can be Googled anyway. The definitions won't make much sense without the necessary background knowledge though so I was just trying to gauge how much the OP knows before giving them. I may as well give a list now, since potential is the main concept that needs to be known. We're allowed to give answers to calculation questions too, but only as a last resort.

1. The difference between the potentials at two points.

2. The potential difference between the terminals(of a cell/battery). It's the actual potential supplied by the battery to the circuit. It's often denoted by r. In a real battery, this is smaller than the emf(when discharging).

3. As above.

4. The resistance within the battery due to the materials of the battery. It decreases the terminal voltage. In many cases it's assumed to be negligible.

5. The potential supplied to electrons as they pass through the cell/battery. It's usually denoted by and called electromotive force.

6. You can work this out using Kirchoff's loop rule(Kirchoff's second law). Imagine the air having infinite resistance. Then you can draw a loop going through the battery, along the wire and around in the air back to the other side of the wire. You then sum the voltage drops and emfs.
You can also use Kirchoff's loop rule in a circuit and derive the equation , then let I tend to 0.
Oh, ok. Thanks!
11. (Original post by morgan8002)

2. The potential difference between the terminals(of a cell/battery). It's the actual potential supplied by the battery to the circuit. It's often denoted by r. In a real battery, this is smaller than the emf(when discharging).
.
Is there some equation to explain this???
12. (Original post by thefatone)
Is there some equation to explain this???
When the cell is discharging, it's connected to a circuit of resistance R, which can be considered for our purposes as a resistor with resistance R. Call the terminal potential difference .
By Ohm's law, the voltage drop inside the cell is Ir and the voltage drop outside the cell is IR. By Kirchoff's loop rule, .

We can also think of the circuit as being a cell with emf and no internal resistance. Repeating the above, .

So . Since r > 0, .
13. (Original post by morgan8002)
When the cell is discharging, it's connected to a circuit of resistance R, which can be considered for our purposes as a resistor with resistance R. Call the terminal potential difference .
By Ohm's law, the voltage drop inside the cell is Ir and the voltage drop outside the cell is IR. By Kirchoff's loop rule, .

We can also think of the circuit as being a cell with emf and no internal resistance. Repeating the above, .

So . Since r > 0, .
i don't really understand *cries
14. (Original post by thefatone)
i don't really understand *cries
Which part?

The circuit looks like this:
15. (Original post by morgan8002)
Which part?

The circuit looks like this:
Wait so since current is resisted against by resistors the overall p.d is less? and emf is the voltage provided by the battery so emf should be more than terminal pd?
16. (Original post by thefatone)
Wait so since current is resisted against by resistors the overall p.d is less? and emf is the voltage provided by the battery so emf should be more than terminal pd?
emf is the max voltage in the case that it were a perfect cell. V=E/Q, voltage is the joules of energy per coulomb of charge. Energy is lost due to overcoming the internal resistance so voltage is lost. The terminal pd is the voltage which the battery is then able to provide after overcoming the internal resistance.
17. (Original post by thefatone)
Wait so since current is resisted against by resistors the overall p.d is less? and emf is the voltage provided by the battery so emf should be more than terminal pd?
Yes. If you mean what I think you mean.

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