Paper 3: Required practical 6 - Internal resistance and emf

Question 1

What is meant by the phrase lost volts?

Answer 1

The difference between the battery’s emf and its terminal potential difference

Question 2

Why should the battery be disconnected between readings?

Answer 2

• The temperature of the circuit should remain constant throughout the experiment, so the resistance in the circuit remains constat
• Disconnecting the battery when not needed mitigates heating

Question 3

Why should you avoid using a rechargeable battery/cell when carrying out this experiment?

Answer 3

Rechargeable power sources have a very low internal resistance which would be hard to measure in this experiment

Question 4

Why should a new cell/battery be used when carrying out this experiment?

Answer 4

• Run-down cells and batteries have inernal resistances that may fluctuate throughout the experiment
• Using a new source will result in a more consistent value, that may therefore be accurately calculated

Question 5

What safety precautions should be taken when carrying out this experiment?

Answer 5

• If connected for long periods of time, the battery and circuitry can become hot
• Avoid touching bare metal contacts and disconnect the battery when readings are not being taken