# Homework Help: What is the value of the loss volt and internal resistance of the battery?

1. May 9, 2008

### looi76

1. The problem statement, all variables and given/known data
When a current of $$2A$$ flows the p.d across a battery's terminal falls from $$12V$$ to $$9V$$.
(a) What is the value of the loss volt?
(b) What is the internal resistance of the battery?

2. Relevant equations
Lost Volt = Ir

3. The attempt at a solution
(a) $$12V - 9V = 3V$$

$$R = \frac{V}{I} = \frac{3}{2} = 1.5$$

$$Lost Volt = 3 \times 1.5 = 4.5$$

Is this correct?

(b) Don't know which equation to use

2. May 10, 2008

### Volcano

your last 4.5 is wrong and no need. It is (lost volt)*(internal rezistance of battery) and meaningless.

Lost volt: 3V
R=1.5 ohm

3. May 10, 2008

### Redbelly98

Staff Emeritus

You can always check by using units in the calculation:
$$3V \times 1.5 \mbox{ohms} = 4.5 \ V\times \mbox{ohms}$$

Since the units (V x ohms) are not Volts, this can't be right.

R = V/I, you already did it without realizing it