# Homework Help: How much work a battery does connected to a resistor

1. Oct 21, 2008

### Marina1234567

1. The problem statement, all variables and given/known data

A battery has an EMF of 12.0 volts and internal resistance of 3 ohms
A 21.0 ohm resistance is connected to the battery.
0.5 Amps flow through the battery, hence 0.5 Amps flows through the 21.0 ohm resistor
The potential difference across the 21 ohm resistor is 10.5 Volts, hence the terminal voltage of the battery is 10.5 Volts.

The question is How much work does the battery connected to the 21.0 ohm resisitor perform in one minute?

2. Relevant equations

Voltage = Joule/coloumb
1 amp = coloumb/ second = (6.258 *10^18 electrons) second
1 electron has a charge -1.60*10^-19 coloumbs

3. The attempt at a solution

current = 0.5 Amps = 3.125*10^18 electron/ second = 30 coloumbs pass wire per minute

usisng the definition of EMF (voltage): 30 coloumbs/ minute * 10.5 volts = 315 Joules

however it keeps on telling me that answer is wrong i know its simple i just can't see it right now thanx

2. Oct 21, 2008

### dlgoff

1 amp x 1 volt = 1 coul/sec x 1 joule/coul = 1 joule/sec = 1 watt

3. Mar 17, 2009

### Satchmo0016

Using the EMF definition, shouldn't you use EMF and not Terminal voltage?

4. Mar 17, 2009

### karkas

My thought on your problem is as follows.
You have a terminal Voltage of 10.5 V, EMF of 12V, Flow of 1/2 A..so pretty much everything you need.

Use the equation for Work on a Resistance : $W=I^2 R t$ where R=r the resistance of the battery. That gives you 45 Joules produced in 60s = 1minute.

I don't take it for granted that I am correct!

5. Mar 17, 2009