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Electricity and Circuits

Current, charge and measuring current

  • 3 things to know
  • Paper 2

Overview

Connecting an ammeter in series, its low resistance, current as the rate of flow of charge, free electrons in a metal, the ampere, and charge from current and time.

What you need to know

Answer each one before you reveal it.

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Key term

Describe how an ammeter is connected, the unit an ammeter reads in, why an ammeter has very low resistance, and define current.

Key term

How must an ammeter be connected to measure the current in a lamp?

Key term

What unit does an ammeter read in?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How must an ammeter be connected to measure the current in a lamp?

    Model answer

    The ammeter is connected in series with the lamp, so that the same current passes through both.

  2. 2

    What unit does an ammeter read in?

    Model answer

    An ammeter reads current in amperes, symbol A.

  3. 3

    Why does an ammeter give a useless reading if it is connected across a lamp instead of in series with it?

    Model answer

    Placed across the lamp it offers an almost resistance-free path, so it measures a large current that bypasses the lamp rather than the current in it.

  4. 4

    Why is an ammeter built to have a very low resistance?

    Model answer

    A very low resistance means that adding the ammeter hardly changes the current it is there to measure.

  5. 5

    Where should an ammeter be placed to measure the total current supplied by a cell to a parallel circuit?

    Model answer

    It is placed in series with the cell, in the main wire before the current splits between the branches.

  6. 6

    What is meant by an electric current?

    Model answer

    An electric current is the rate of flow of electric charge.

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ALength is measured in metres, with the symbol m.
BMass is measured in kilograms, symbol kg.
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