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The motor effect
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A wire carrying current in a magnetic field feels a force. This is how electric motors work.
The motor effect
When a current-carrying wire is in a magnetic field, the two fields interact and the wire feels a force.
The force is biggest when the wire is at right angles to the field. There is no force if the wire is parallel to the field.
The force is biggest when the wire is at right angles to the field. There is no force if the wire is parallel to the field.
Fleming's left-hand rule
First finger: Field (north to south).
Second finger: Current (positive to negative).
Thumb: Motion (the force).
Reversing the current or the field reverses the force.
Second finger: Current (positive to negative).
Thumb: Motion (the force).
Reversing the current or the field reverses the force.
Calculating the force (Higher)
F = B × I × l: force (N) = magnetic flux density (T) × current (A) × length of wire in the field (m).
In a motor, a coil feels forces in opposite directions on each side, so it turns. A split-ring commutator keeps it turning the same way.
In a motor, a coil feels forces in opposite directions on each side, so it turns. A split-ring commutator keeps it turning the same way.
A 0.05 m wire carries 4 A at right angles to a 0.2 T field. Find the force.
- F = B × I × l
- F = 0.2 × 4 × 0.05
Answer: 0.04 N
Current in a magnetic field gives a force. Fleming's left-hand rule gives the direction. F = BIl. Motors use the force to make a coil spin.
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