Internal Resistance

For this Virtual Lab you will need to use the PHeT Circuit Simulator

If you haven't used it before then spend a few minutes creating a couple of simple circuits including a voltmeter and ammeter.

Internal Resistance: Effectively a small resistor inside the battery

Create the following circuit 

With the leads of the voltmeter across one end of the battery and the opposite end of the 0 Ωresistor, the potential difference should be 9.0V 

1. Remove one of the voltmeter leads from the circuit.
2. Right click on the resistor and select "Change Resistance" (the pop-up box should be moved so that it is not overlapping the voltmeter).
3. Increase the resistance of the resistor to 50 Ω.
4. Reconnect the loose voltmeter lead to the circuit.

Questions

• If the resistance of the resistor is decreased or increased, will the reading on the voltmeter change? If so, how? 
• How would your answers change if the circuit were open? 
• What happens if both resistors are set to zero in a closed circuit?

Now remove the resistor near the battery and replace the void with a wire to complete the circuit. Right click on the battery to reveal how its internal resistance can be changed.The only difference now is that the probes of a voltmeter can't be 'snuck' in, avoiding the internal resistance as done up to now. Such is the case with real batteries.

1. Set The Battery Internal Resistance to 0.75Ω
2. Set the top resistor to 0Ω  
3. Ensure the voltmeter is across the battery
4. Open the slider to change the bottom resistors resistance you are going to change it from in 10 steps 100 Ω to 0 Ω .. (BEFORE YOU DO!) What do you think will happen to the voltage and current?. Now try is and see if you are correct. 
5. In a spreadsheet Record  your 10 Voltages and currents. Plat a graph of V vs I. What value does the gradient have?
6. Repeat the process with a couple ofdifferent internal resistances. ensure you understand what is happening.