The Motor Effect

What is the motor effect?

When a current carrying a conductor is placed in a magnetic field it experiences a force.

What is the motor effect caused by?

The field created by the current interacting with the magnetic field.

How can a force created by the motor effect be increased?

Increasing:

• The size of the current.

• The length of the conductor in magnetic field

• The flux density.

What is the equation for force?

Force = Magnetic Flux Density x Current x Length (of wire)

What will reversing the direction of either the current of the magnetic field cause?

The direction of the force to reverse.

How can you find the direction of the force on the conductor using Fleming’s left hand rule?

1. Hold left hand so that thumb, first finger and second finger are all at right angles to one another.

2. Align first finger, so that it points in direction of the magnetic field, from north to south.

3. Rotate wrist so that second finger points along wire in direction current is flowing.

4. Thumb will be pointing in direction of the force i.e. direction the conductor would move.

What can Fleming’s left hand rule be used to find?

Direction of either :

• Field.

• Current.

• Movement.

As long as the other two are know.

Why does a current carrying coil in a magnetic field rotate?

The current going up one side of the coil is the opposite direction to the current coming back down the other side, so one side moves up and other moves down.

How are electrical motors designed?

So that the coil rotates continuously.

Why do the brush contacts at the commutator ensure in an electrical motor?

That the current direction in the coil is always the same direction. Ensures the motor continues rotating and doesn’t simply stop in an upright position.

How can Fleming’s left hand rule be used on one side of the coil to work out which direction the motor will rotate?

• Increasing current or magnetic field makes motor rotate faster.

• Reversing current or magnetic field makes motor rotate in opposite direction.