Internal resistance

Question 1

Describe how you would calculate internal resistance?

Answer 1

Set up a circuit, voltmeter in parallel with cell with internal resistance, in series with a switch, ammeter and variable resistor.

• Close the switch, record the potential difference and the current and adjust resistance using variable resistor, take six readings of current six of voltage.
• Plot a graph, V-I, The y-intercept is e.m.f and gradient is -r (internal resistance).

Question 2

High or low internal resistance?

Answer 2

Rechargeable batteries in mobile phones and laptops have low internal resistance, allowing them to be recharged using higher currents without overheating or wasting energy.

In contrast, the high-voltage power supplies used in classrooms have a very high internal resistance, acting as a safety feature, preventing the power supply from delivering a fatal current.

Question 3

How can the terminal p.d be decreased?

Answer 3

In normal use, the e.m.f does not change. However, changing the current affects the lost volts and the terminal p.d. Increasing the current means that more charges travel through the cell each second and so more work is done by the charges, increasing the lost volts - lowering the terminal p.d.

Question 4

What is internal resistance?

Answer 4

internal resistance is the resistance within a battery or power supply that opposes the flow of current.