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Electricity

Electromotive force and internal resistance

  • 6 things to know
  • Papers 1 and 3

Overview

Emf, terminal potential difference, lost volts, and measuring both experimentally.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Numbers

What is emf, how is it defined by energy and charge, and what unit is it in?

Numbers

How is the volt expressed in joules and coulombs, and what is internal resistance?

Numbers

What is terminal potential difference, and how does it relate to emf?

Numbers

Why is terminal potential difference less than emf, and when are they equal?

Numbers

What are lost volts, and how are they calculated?

Numbers

How is current found in a circuit with internal resistance, and how is emf measured?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is the definition of electromotive force (emf)?

    Model answer

    Electromotive force is the energy transferred per unit charge by a source in driving charge around a complete circuit.

  2. 2

    State the formula that defines electromotive force in terms of energy and charge.

    Model answer

    ε = E/Q, where ε is emf, E is energy transferred, and Q is charge.

  3. 3

    What is the unit of electromotive force?

    Model answer

    The volt (V).

  4. 4

    Express the volt in terms of the units of energy and charge.

    Model answer

    One volt is equivalent to one joule per coulomb (J C⁻¹).

  5. 5

    Define internal resistance.

    Model answer

    Internal resistance is the resistance within the power supply itself that opposes current flow.

  6. 6

    Where is internal resistance located in a circuit?

    Model answer

    Internal resistance is located inside the power supply or cell itself.

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