The force on a current in a magnetic field, Fleming's left-hand rule, F = BIl with the tesla, and why the coil of a motor keeps turning.
What you will learn
- Find the direction of the force with Fleming's left-hand rule
- Calculate the force with F = BIl, changing mT, mA and cm first (Higher)
- Explain how a d.c. motor turns and what makes it faster
Two fields, one push
Put a wire carrying a current in the field of a magnet.
The wire's own field and the magnet's field interact, and the wire feels a force. That is the motor effect.
Fleming's left-hand rule. Hold your left thumb, first finger and second finger at right angles:
- First finger: Field (N to S)
- seCond finger: Current
- thuMb: Motion (the force)
Reverse the current or the field and the force reverses. Reverse both and it is back as before. The force is directly proportional to the current: double the current (or the field) and the force doubles. A wire lying along the field lines feels no force.
The rest of this lesson and its 10 practice questions are locked.
In this lesson
- Two fields, one push
- How big is the force? (Higher)
- The electric motor
- Try it: Your first F = BIl
10 practice questions, marked as you go; about 25 minutes in all.
Key terms
Motor effect, Fleming's left-hand rule, Along, Tesla, Opposite directions, Split-ring commutator, Brushes, Loudspeaker, Faster
In this unit: Magnetism and electromagnetism
Magnets and field lines, electromagnets, the motor effect and F = BIl, then loudspeakers, generators, microphones and transformers.