# Internal resitance and electromotive force

## Homework Statement

1) a complete circuit consists of a 12.0 V battery with a 4.50 ohm resistor and switch. the internal resistance of the battery is 0.30 ohms when switch is open. what does the voltmeter read when placed:

a. across the terminal of the battery when the switch is open
b. across the resistor when the switch is open
c. across the terminal of the battery when the switch is closed
d. across the resistor when the switch is closed

2) when the switch S is open, the voltmeter V reads 2.0 V. when the switch is closed, the voltmeter reading drops to 1.50 V and the ammeter reads 1.20 A. find the emf (electromotive force) and the internal resistance of the battery. assume that the two meters are ideal so they don't affect the circuit.

## Homework Equations

Terminal Potential Difference= -Ir+ electromotive force
Terminal Potential Diff= IR
emf=W/q

## The Attempt at a Solution

@1 would it be Terminal Voltage= IR? but i kinda don;t know how to apply it with the voltmeter placed in different places.

Just do it the same way as the first one. You can treat the internal resistance as a separate resistor.

vk6kro