In terms of energy transfer direction, how does e.m.f. differ from p.d.?

E.m.f. is the energy transferred per unit charge from the source to the charge carriers, whereas p.d. is the energy transferred per unit charge from the charge carriers to the circuit components.

State the equation for energy transferred by a source in terms of e.m.f. and charge.

W = EQ, where W is energy transferred, E is e.m.f., and Q is charge.

Calculate the energy transferred when e.m.f. = 1.5 V, charge = 8.5 C.

Energy transferred = 1.5 × 8.5 = 12.8 J.

OCR A-Level Physics A H556

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Energy, Power and Resistance

Energy transfer in circuits

3 things to know
Papers 2 and 3

Overview

Recall questions on W = VQ and W = EQ, and on the energy gained by a charge accelerated through a potential difference.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

The symbol E is used for e.m.f. Name three other quantities that also use the symbol E, which must not be confused with e.m.f.

Key term

When we say a component has a p.d. across it, in which direction is energy being transferred?

Key term

State the equation relating energy transferred, potential difference, and charge.

Questions from this subtopic

Each one with the model answer underneath.

1
The symbol E is used for e.m.f. Name three other quantities that also use the symbol E, which must not be confused with e.m.f.
Model answer
Energy, electric field strength, and Young modulus.
2
In terms of energy transfer direction, how does e.m.f. differ from p.d.?
Model answer
E.m.f. is the energy transferred per unit charge from the source to the charge carriers, whereas p.d. is the energy transferred per unit charge from the charge carriers to the circuit components.
3
When we say a component has a p.d. across it, in which direction is energy being transferred?
Model answer
Energy is transferred from the charge carriers to the component.
4
State the equation relating energy transferred, potential difference, and charge.
Model answer
W = VQ, where W is energy transferred, V is potential difference, and Q is charge.
5
State the equation for energy transferred by a source in terms of e.m.f. and charge.
Model answer
W = EQ, where W is energy transferred, E is e.m.f., and Q is charge.
6
Calculate the energy transferred when e.m.f. = 1.5 V, charge = 8.5 C.
Model answer
Energy transferred = 1.5 × 8.5 = 12.8 J.

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