| How can you get a higher magnetic field of a wire with current flowing through it? | 1)Increase the current
2)Get closer to the wire |
| What is a soleonoid? | 1)A straight coil of wire which can carry an electric current to create a magnetic field.
2)The field is similiar to the field of a bar magnet and is strong and uniform.
3)The small magnetic fields caused by the current in each coil add together to make a stronger overall magnetic field. |
| What is an electromagnet? | A solenoid (straight coil of wire) with an iron core is called an electromagnet. he iron core increases the solenoid’s magnetic field strength. |
| What is the motor effect? | The effect where force is exerted on a wire carrying a current in a magnetic field |
| How can we increase the force of a given length of wire in a magnetic field? | 1)Increase current
2)Increase magnetic field strength |
| When is the force greatest? | When the current is 90degrees to the direction of magnetic field |
| What does Flemings left hand rule show? | The direction of a motor effect force.
1)the forefinger is lined up with magnetic field lines pointing from north to south
2)the second finger is lined up with the current pointing from positive to negative
3)the thumb shows the direction of the motor effect force on the conductor carrying the current |
| Explain how electric motors work. | Starting from the position shown in the diagram of the dc motor:
1)current in the left hand part of the coil causes a downward force, and current in the right hand part of the coil causes an upward force
2)the coil rotates anticlockwise because of the forces described above
When the coil is vertical it moves parallel to the magnetic field, producing no force. This would tend to make the motor come to a stop, but two features allow the coil to continue rotating:
3)the momentum of the motor carries it on round a little
4)a split ring commutator changes the current direction every half turn
Once the conducting brushes reconnect with the commutator after a half turn:
5)current flows in the opposite direction through the wire in the coil
6)each side of the coil is now near the opposite magnetic pole
This means that the motor effect forces continue to cause anticlockwise rotation of the coil. |
| How does a loudspeaker work? | 1)a current in the coil creates a n electrimagnetic field
2)the electromagnetic field interacts with the permanent magnet generating a force pushing the cone outwards
3)the current is made to flow in the opposite direction
4)the direction of the magnetic field reverses
5)the force on the cone now pulls it back in
6)repeated alternation of current direction causes the cones to vibrate in and out
7)cone vibration cause pressure variations in air which are spound waves |
