Define electromotive force (e.m.f) .

The amount of chemical energy converted to electrical energy per coulomb of charge when it passes through a power supply, measured in volts .

Define internal resistance .

The resistance of the materials within the battery (or cell).

How is e.m.f measured experimentally?

By connecting a high-resistance voltmeter in parallel with the cell in an open circuit (no current flowing).

If an exam question states a battery has .......... internal resistance, the e.m.f is equal to its terminal voltage.

If an exam question states a battery has negligible internal resistance, the e.m.f is equal to its terminal voltage.

In the required practical investigating e.m.f and internal resistance, what are the independent and dependent variables?

Independent variable: resistance , R Dependent variables: voltage , V , and current , I

What two variables must be controlled in the e.m.f and internal resistance required practical?

The e.m.f of the cell The internal resistance of the cell

When plotting V against I for this experiment, what do the gradient and y-intercept represent?

Gradient = negative internal resistance , − r Y-intercept = e.m.f , E

Why should the switch only be closed for as long as it takes to take each pair of readings?

To prevent the internal resistance of the cell from changing (heating up) during the experiment — this reduces systematic error .

Give two ways to reduce random error in the e.m.f and internal resistance required practical.

Use fairly new cells Wait for the voltmeter and ammeter readings to stabilise before recording Take at least three repeat readings and calculate a mean

The cell and the resistor, labelled r , should be connected in .......... and considered to be a single cell.

The cell and the resistor, labelled r , should be connected in series and considered to be a single cell.

True or False? In this experiment, at least eight to ten readings of V and I should be taken across the whole range of the variable resistor.

True. A minimum of eight to ten readings should be taken, varying the resistance across its whole range.

State two safety considerations for the e.m.f and internal resistance required practical.

Electrical components can get hot during prolonged use Switch off the power supply immediately if you smell burning Keep liquids away from the equipment

A LevelPhysicsAQAFlashcardsElectricityElectromotive Force & Internal Resistance

Electromotive Force & Internal Resistance (AQA A Level Physics): Flashcards

Exam code: 7408

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Define electromotive force (e.m.f).

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Cards in this collection (15)

Define electromotive force (e.m.f).
The amount of chemical energy converted to electrical energy per coulomb of charge when it passes through a power supply, measured in volts.
Define internal resistance.
The resistance of the materials within the battery (or cell).
Define lost volts.
The work done per unit charge to overcome the internal resistance of a battery when current flows:
$v = ε - V = I r$
How is e.m.f measured experimentally?
By connecting a high-resistance voltmeter in parallel with the cell in an open circuit (no current flowing).
Write the equation relating e.m.f, current, load resistance and internal resistance.
$ε = I (R + r)$
If an exam question states a battery has .......... internal resistance, the e.m.f is equal to its terminal voltage.
If an exam question states a battery has negligible internal resistance, the e.m.f is equal to its terminal voltage.
True or False?
The terminal potential difference of a cell is always equal to its e.m.f.
False.
Because a cell has internal resistance, the terminal p.d. is always lower than the e.m.f — the difference is the lost volts, $I r$ .
In the required practical investigating e.m.f and internal resistance, what are the independent and dependent variables?
- Independent variable: resistance, R
- Dependent variables: voltage, V, and current, I
What two variables must be controlled in the e.m.f and internal resistance required practical?
- The e.m.f of the cell
- The internal resistance of the cell
When plotting V against I for this experiment, what do the gradient and y-intercept represent?
- Gradient = negative internal resistance, −r
- Y-intercept = e.m.f, E
Why should the switch only be closed for as long as it takes to take each pair of readings?
To prevent the internal resistance of the cell from changing (heating up) during the experiment — this reduces systematic error.
Give two ways to reduce random error in the e.m.f and internal resistance required practical.
- Use fairly new cells
- Wait for the voltmeter and ammeter readings to stabilise before recording
- Take at least three repeat readings and calculate a mean
The cell and the resistor, labelled r, should be connected in .......... and considered to be a single cell.
The cell and the resistor, labelled r, should be connected in series and considered to be a single cell.
True or False?
In this experiment, at least eight to ten readings of V and I should be taken across the whole range of the variable resistor.
True.
A minimum of eight to ten readings should be taken, varying the resistance across its whole range.
State two safety considerations for the e.m.f and internal resistance required practical.
- Electrical components can get hot during prolonged use
- Switch off the power supply immediately if you smell burning
- Keep liquids away from the equipment

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