# Voltage, Current

1. Nov 15, 2006

### Air

Can I have some information about these topics?

• Voltage
• Current
• Resistance
• Internal Resistance

2. Nov 15, 2006

### leright

You need to be a little more specific.

3. Nov 15, 2006

### wxrocks

Last edited by a moderator: Apr 22, 2017
4. Nov 15, 2006

### Staff: Mentor

Questions that general/vague will at best get you a reference to google or a wik link. You'll need to be more specific if you want some actual answers.

5. Nov 15, 2006

### Mindscrape

Voltage = potential difference between two points
Current = rate of change of charge with time
Resistance = proportional to the voltage and inversely proportional to current
Internal Resistance = Thevenin resistance seen by outside source

6. Nov 16, 2006

### Air

Thank You. I needed information like this.

7. Nov 16, 2006

### Air

What is Internal Resistance in relation to EMF?

8. Nov 16, 2006

### Agnostic

Think of it analogous to water flowing from an elevated tank through a small hose.

Voltage is the pressure behind the water which corresponds to amount of water in the tank pushing down.

Current is the speed of the water.

Resistance is something in the hose obstructing the path of water flow.

Internal resistance is the resistance of the water having friction with pipe walls.

9. Nov 19, 2006

### Air

Thats a very good analogy. Thanks.

______________________________________________________

What is Internal Resistance in relation to EMF?

10. Nov 19, 2006

### NoTime

What do you mean by internal resistance?
Do you disagree with Mindscrape's definition?

E=IR

11. Nov 19, 2006

### Gza

Well, if you have a given EMF, generated by a magnetic field changing in time, and are near some circuit or wire, you can just use good ol' ohms law to find the resistance:

V=IR, or using different notation for your EMF, EMF=IR, or R=EMF/I, so the reistance in the circuit is proportional to the strength of the EMF, and inversely proportional to current.

12. Nov 22, 2006

### Air

The Voltage that is lost in the Power supply.

13. Nov 22, 2006

### NoTime

Usually, for most things, it's negligable.
For actively regulated power supplys it can be 0 or even negative.

If it is a factor, then the power supply resistance gets added to the rest of the resistance in the circuit.

14. Nov 23, 2006

### Air

Does this affect the circuit in any way?

15. Nov 23, 2006

### Hootenanny

Staff Emeritus
Yes, in exactly the same way a normal resistor would. Suppose you have a cell with a 12V emf and 1$\Omega$ internal resistance. This would be equivalent to a circuit containing a 12V cell with no internal resistance, in series with a 1$\Omega$ resistor.

16. Nov 23, 2006

### Air

I see.

Is it dangerous if the resistance gets high? If so why and what happens?

17. Nov 23, 2006

### Hootenanny

Staff Emeritus
Resistors dissipate energy, how do you suggest they do this?

18. Nov 23, 2006

### Air

Resistance serves to limit the amount of Current through the circuit with a given amount of Voltage supplied by the battery.

19. Nov 23, 2006

### Hootenanny

Staff Emeritus
Yes, it does this by dissipating (removing) energy (from the circuit). This energy is dissipated as heat. Therefore, if you have a high resistance together with a high current flow, then large amounts of heat will be dissipated.

20. Nov 26, 2006

### Air

After lots of heat is dissipated, does the Resistance, Voltage or Current change (i.e go lower or higher)?

I thank all the people who have helped me so far. You have increased my knowledge.