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Electric and Magnetic Fields

Equipotentials, field diagrams and work done

  • 1 thing to know
  • Papers 1 and 3

Overview

Recall questions on what an equipotential is, the angle it makes with field lines, why field lines never cross, and the work done moving a charge through a potential difference.

What you need to know

Answer each one before you reveal it.

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Numbers

How do field strength and potential differ with distance, what work is done moving a charge, and why can field lines never cross?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How much work is done in moving a charge along an equipotential, and why?

    Model answer

    No work is done, because there is no change in potential and hence no change in the charge's potential energy.

  2. 2

    What angle do field lines make with equipotentials?

    Model answer

    They always cross at right angles, that is at 90°.

  3. 3

    What shape are the equipotentials around an isolated point charge, and how are they spaced?

    Model answer

    They are concentric circles, or spheres in three dimensions, centred on the charge, and for equal steps in potential they become more widely spaced further out.

  4. 4

    What do the equipotentials in the uniform field between two parallel plates look like?

    Model answer

    They are straight lines parallel to the plates and equally spaced for equal steps in potential.

  5. 5

    Why can two electric field lines never cross?

    Model answer

    Because the field at any point has only one direction, so only one line can pass through that point.

  6. 6

    State the equation for the work done when a charge moves through a potential difference:

    Model answer

    W = QΔV, where Q is the charge moved and ΔV is the potential difference.

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