Chapter notes

Question 1

Finding out the field direction from current in a wire

Answer 1

Right-hand grip rule

Question 2

What is the motor effect?

Answer 2

When the current flowing in a wire in a magnetic field which the current is not parallel to so a force is exerted on the wire

Question 3

In a motor, how can the direction of the force be reversed? (Two points)

Answer 3

1. Reversing the direction of the current
2. Reversing the direction of the field, by turning it around

Question 4

How does Flemings left hand rule work?

Answer 4

thumb-motion (forces)
first- field
second- current

Question 5

Electric motors are designed to…

Answer 5

…use the motor effect to create a turning movement.

Question 6

At what position is there no forces acting on the wire?

Answer 6

Vertical position. Reliant on momentum to carry itself further round. The forces have no turning effect.

Question 7

How can the turning effect be increased in motors?

Answer 7

-turns
-current
-field

Question 8

What does a commutator do?

Answer 8

Makes sure the current flows the same way. Every half-turn, the commutator reverses the connections to the power supply.

Question 9

With beams of electrons, which rule is used?

Answer 9

Flemings left-hand rule

Question 10

What should you remember when using the rule for beams of electrons?

Answer 10

Electron flow is in the opposite direction of conventional current.

Question 11

How can the force on the beam of electrons be reversed?

Answer 11

By reversing the field.

Question 12

What is the electron beam effect used in?

Answer 12

Particle accelerators, to focus and divert beams of charged particles. These particles have a lot of kinetic energy and travel at enormously high speeds. Huge fields are used to divert them.

Question 13

What do all generators have in common?

Answer 13

• a magnetic field (prod by magnets or electromagnets)
• a coil of wire (fixed or moving)
• movement (coil and field move relative to each other)

Question 14

Describe the power station process.

Answer 14

…The coil inside the generator spins around in the inside of fixed electromagnets, which provide the field. Large current is induced in the rotating coil.

Question 15

If the generator is connected to a complete circuit…
If it is not…

Answer 15

..induced current flows
..induced e.m.f/voltage will be at its ends ready to make current flow around the circuit.

Question 16

What is induced e.m.f?

Answer 16

The e.m.f created in a conductor when it cuts through field lines

Question 17

What is electromagnetic induction?

Answer 17

the production of an e.m.f across an electrical conductor when there is relative movement between the conductor and the field.

Question 18

In terms of electromagnetic induction, describe what happens with a wire and magnet.

Answer 18

-Wire is moved upwards and downward, so a current flows. (current flows in an opposite direction). -Magnet can be moved instead.

Question 19

In terms of electromagnetic induction, describe what happens to a coil and magnet.

Answer 19

Reverse the magnet, to reverse the current.
If the magnet is stationary next to the coil, no current flows.

Question 20

A centre-zero menter

Answer 20

Needle to the left, the current flows one way, to the right the other way

Question 21

How do you increase induced e.m.f?

Answer 21

-Stronger magnet
-move wire more quickly
-turns

Question 22

[Induction and field lines] What does the cutting rule tell us?

Answer 22

further away –> fewer lines –> smaller e.m.f

quicker–> cut more quickly–> bigger e.m.f

more turns–> bigger e.m.f

Question 23

How do you determine the direction of force, field and current when it comes to electromagnetic induction?

Answer 23

Fleming’s right-hand rule

Question 24

What does a slip ring do in an a.c generator?

Answer 24

They rotate with the coil while the brushes rub against them. The brushes therefore have the same e.m.f as the sides of the coil.

Question 26

What are slip-rings?

Answer 26

Device used to allow current to and from the a.c generators’ coil.

Question 27

How do you increase the voltage generated in an a.c generator?

Answer 27

-turn more rapidly
-turns of wire
-coil with bigger area
-stronger magnets