## Monday, May 25, 2009

### 3.2 THE FORCE ON A CURRENT-CARRYING CONDUCTOR IN A MAGNETIC FIELD

You should able to answer the following questions .

1. Describe whathappens to current-carrying conductor in a magnetic field
• An electric current produces a magnetic field around it.

• When a wire carries an electric current through another magnetic field, a force is exerted on the wire.
• The magnetic force on a current-carrying conductor is in a magnetic field is due to the combination of the magnetic field due to the current in the conductor and the external
magnetic field to produce a resultant magnetic field( or knows as The Catapult Field).

2. How would you determine the direction of the magnetic force acting on the wire?

The direction of the magnetic force, F, acting on the wire can be determined by using Fleming’s left-hand rule.

3. What is Fleming’s Left – Hand Rule ?

If the forefinger, second finger and the thumb of the left hand are extended at right angles to each other, with the forefinger in the direction of the magnetic field, the second finger in the direction of the current, then the thumb will point the direction of the force, F or motion.

4. Explain the factors that affect the magnitude of the force on a current-carrying conductor in a magnetic field.

The magnitude of the force on a current-carrying conductor in a magnetic field depends on:
i. the size of the current in the conductor
ii. the strength of the magnetic field.

5. Describe how a direct current motor works

Commutator: reverse the direction of current in the coil every half rotation so that the coil continues to turn in same direction

Carbon Brush: to contact with the commutator so the current from the battery enters the coil.

Spring: push the brush so it will always contact with the commutator.

The direct current motor (d.c. motor) uses the turning effect on a current-carrying coil in a magnetic field.

when current flows in the coil placed in a magnetic field, a pair of forces which are equal in magnitude but opposite in directions is produced.

The forces act on the opposite segments of the current-carrying coil in a magnet field and provide the turning effects that cause the motor to rotate.

video source : http://web.ncf.ca/ch865

6. How to increase the speed of rotation of the motor.

i. Increasing the size of the current

ii. Increasing the strength of the magnetic field

iii. increasing the number of turns

iv. Increasing the area of the coil