AQA · GCSE · Physics

    Course version: 8463 · Version from Sept 2016

    A second charged object placed in the field experiences a force.

    Full specification wording

    Electric fields: A second charged object placed in the field experiences a force.

    The field is only detectable through what it does to another charge.

    Checked against the AQA 8463 specification (opens in a new tab) on .

    • Point 4 of 6
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    The field is only detectable through what it does to another charge. Place a second charged object in the field and it feels a force: away from the first object if the two charges are alike, towards it if they are opposite. The direction of the field line at that point gives the direction of the force on a positive charge, and a negative charge feels a force in the opposite direction to the line. The size of the force depends on how strong the field is at that point and on how much charge the second object carries, so the same object feels a larger force nearer the first charge. This is what non-contact force means in practice: the first object sets up the field, and the second responds to the field where it sits.

    What earns the marks

    • The second charged object experiencing a force when placed in the field.
    • The direction of that force depending on whether the charges are alike or opposite.
    • The force being larger where the field is stronger.
    • The field line direction giving the direction of the force on a positive charge.

    Common mistakes and how to put them right

    • Saying the second object must touch a field line before a force can act.

    • Giving the force on a negative charge in the same direction as the field line.

    • Assuming the force is the same size everywhere in the field.

    • Describing the second object as attracted in all cases, whatever its charge.

    Exam tips

    • Note the sign of the test charge before deciding the direction of the force.
    • Quote both factors when asked what the force depends on: field strength and the charge placed in it.
    • Use the field-line arrow for a positive charge, then reverse it for a negative one.

    Try the lesson

    The start of the Electric fields: A second charged object placed in the field experiences a force. lesson, made from checked teaching notes for this specification point.

    Have a go first

    What happens to a second charged object when it is placed in the electric field of another charged object?

    Listen

    The field is only detectable through what it does to another charge. Place a second charged object in the field and it feels a force: away from the first object if the two charges are alike, towards it if they are opposite. The direction of the field line at that point gives the direction of the force on a positive charge, and a negative charge feels a force in the opposite direction to the line. The size of the force depends on how strong the field is at that point and on how much charge the second object carries, so the same object feels a larger force nearer the first charge. This is what non-contact force means in practice: the first object sets up the field, and the second responds to the field where it sits. A strong answer earns marks for these points. the second charged object experiencing a force when placed in the field. the direction of that force depending on whether the charges are alike or opposite. the force being larger where the field is stronger. the field line direction giving the direction of the force on a positive charge. Exam tip: Note the sign of the test charge before deciding the direction of the force.

    See it

    A top-down flowchart. The first charged object sets up the field, leading to a second charged object being placed in the field, which leads to the second object experiencing a force. From this, the direction depends on whether the charges are alike or opposite: alike gives a force away from the first object, opposite gives a force towards it. Also from the force, the field line direction gives the force direction on a positive charge, and a negative charge feels a force opposite to the line. Finally, the size of the force depends on field strength and charge carried, giving a larger force nearer the first charge.
    It shows how the first object sets up the field, the second charged object then feels a force, and how the direction and size of that force are determined.

    Key words

    Say what each word means before you turn the card.

    test charge

    Try answering aloud or in your head before turning the card.

    direction of force

    Try answering aloud or in your head before turning the card.

    field strength

    Try answering aloud or in your head before turning the card.

    non-contact interaction

    Try answering aloud or in your head before turning the card.

    See every definition
    test charge
    A second charged object placed in the field, which experiences a force and is used to detect the field.
    direction of force
    Given by the field line at that point for a positive charge, while a negative charge feels a force in the opposite direction to the line.
    field strength
    How strong the field is at that point, which together with the charge the second object carries determines the size of the force.
    non-contact interaction
    The first object sets up the field, and the second responds to the field where it sits, so a force acts across a gap between two objects.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. The first charged object sets up the field, leading to a second charged object being placed in the field, which leads to the second object experiencing a force. From this, the direction depends on whether the charges are alike or opposite: alike gives a force away from the first object, opposite gives a force towards it. Also from the force, the field line direction gives the force direction on a positive charge, and a negative charge feels a force opposite to the line. Finally, the size of the force depends on field strength and charge carried, giving a larger force nearer the first charge.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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