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Electricity and Circuits

Designing circuits to test components

  • 2 things to know
  • Paper 2

Overview

Placing a switch, ammeter, variable resistor and protective resistor in series with a voltmeter across the component, and circuits for a filament lamp, a diode, a thermistor and a light-dependent resistor.

What you need to know

Answer each one before you reveal it.

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Key term

Why is a series circuit convenient for measuring the current in a component?

Key term

Why must a voltmeter be added across a component rather than into the series loop when a series circuit is used for measurements?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Why is a switch placed in series in a circuit that is being tested?

    Model answer

    In series the switch breaks the single path, so one switch turns the whole circuit on and off.

  2. 2

    Where should an ammeter and a variable resistor be placed in a series test circuit?

    Model answer

    Both are placed in series in the main loop, so that the same current passes through them and the component being tested.

  3. 3

    Why is a series circuit convenient for measuring the current in a component?

    Model answer

    The current is the same everywhere in a series circuit, so the ammeter can be placed anywhere in the loop.

  4. 4

    Why must a voltmeter be added across a component rather than into the series loop when a series circuit is used for measurements?

    Model answer

    The voltmeter needs the potential difference of that one component across it, which only happens when it is in parallel with the component.

  5. 5

    What is the purpose of including a variable resistor in a series test circuit?

    Model answer

    It allows the current and the potential difference to be changed so that a range of readings can be taken.

  6. 6

    Why is a series circuit unsuitable for testing several lamps if the rest must stay lit while one of them is checked?

    Model answer

    A break or an open switch anywhere in a series circuit stops the current in all of the lamps.

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