Latest revision as of 14:08, 20 April 2010

Specification References

6.11 appreciate that there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field
6.12 recall that a force is exerted on a current-carrying wire in a magnetic field, and how this effect is applied in simple d.c.electric motors and loudspeakers
6.13 use the left hand rule to predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field
6.14 recall that the force on a current-carrying conductor in a magnetic field increases with the strength of the field and with the current

Show them the wire hanging between the two poles of magnet and switch on current. Let them discuss what happens.
Reverse polarity, direction of current and let them analyze what happens.
Have ready one of the little motors and tell them that they will have to be building one themselves

Discuss why the wire moves when current is flowing through it: the magnetic field of the permanent magnet reacts with the magnetic field of the current in the wire.
This interaction between the two magnetic fields is shown by the presence of the electromagnetic force acting on the wire; under the action of the electromagnetic force, the wire moves.
The direction of the electromagnetic force is given by FLEMING’s LEFT HAND RULE:
- Hold your left hand and spread out the thumb, first and second finger so that they are at right angles to each other.
- Point your First Finger in the direction of the magnetic Field (N to S)
- Rotate your hand about that finger until your seCond finger points in the direction of Current ( + to -)
- THEN thumb points in the direction on the movement of the wire (direction of the electromagnetic force)

The movement of the current-carrying wire into a magnetic field is called the MOTOR EFFECT.
Discuss ways in which the turninh effect on the coil/wire could be increased.
Use the 'electric motor' worksheet(Science Shared area) to show how Fleming’s left hand rule applies.
Complete the worksheet
Show them how the moving-coil loudspeaker works and students build their own.

Large Motor demo, small motor demo, Force on a wire demos, Open loudspeaker demo, Making a loudspeaker kit- class practical

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 * This interaction between the two magnetic fields is shown by the presence of the electromagnetic force acting on the wire; under the action of the electromagnetic force, the wire moves.
 * The direction of the electromagnetic force is given by FLEMING’s LEFT HAND RULE:
-•	Hold your left hand and spread out the thumb, first and second finger so that they are at right angles to each other.
+**Hold your left hand and spread out the thumb, first and second finger so that they are at right angles to each other.
-•	Point your First Finger in the direction of the magnetic Field (N to S)
+**Point your First Finger in the direction of the magnetic Field (N to S)
-•	Rotate your hand about that finger until your seCond  finger points in the direction of Current ( + to -)
+**Rotate your hand about that finger until your seCond  finger points in the direction of Current ( + to -)
-•	THEN thumb points in the direction on the movement of the wire (direction of the electromagnetic force)
+**THEN thumb points in the direction on the movement of the wire (direction of the electromagnetic force)
 * The movement of the current-carrying wire into a magnetic field is called the MOTOR EFFECT.