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1. Describe and interpret an experiment to show that a force acts on a current-carrying conductor in a magnetic field, including the effect of reversing:
• the current
• the direction of the field

If a wire carrying a current is placed in a magnetic field (with lines of force at right angles to the wire) then it will experience a force at right angles to both the current direction and field lines.

The force on the wire is increased if:

• The current is increased
• A stronger magnet is used
• The length of the wire in the field is increased

1. State and use the relative directions of force, field and current.

To predict the direction of the force, current or fields we can use Fleming’s left-hand rule:

So when reversing the current or direction of fields, the direction of force also changes. You can use the above rule to figure out the exact change. Try this question for practice and check the answer below.

(Hint: a magnetic field always runs from north to south)

ANSWER:
Downwards
Between the magnets, the current is flowing in the north direction, away from us (not the magnet’s north!), so you point your second finger away from you.
The magnetic field runs from the north pole of the magnet to its south pole, i.e. from the left to the right and so point your forefinger in that direction. Don’t change the position of your second finger accidentally!
And so naturally your thumb which indicates current will be in the downward position!

Notes submitted by Lintha

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