Topic 12 - Magnetism And The Motor Effect

Question 1

At which part of a magnet are the magnetic forces strongest?

Answer 1

The poles

Question 2

What type of force is exerted if two like poles of a magnet are brought near each other?

Answer 2

They repel each other

Question 3

What type of force is exerted if two unlike poles of a magnet are brought near each other?

Answer 3

They attract each other

Question 4

What is a magnetic field?

Answer 4

The region surrounding a magnet where another magnet or magnetic material experiences a non-contact force

Question 5

What is the difference between a permanent magnet and an induced magnet?

Answer 5

A permanent magnet produces its own magnetic field

An indices becomes magnetic when placed in a magnetic field

Question 6

What type of force is always caused by induced magnetism?

Answer 6

Attraction

Question 7

Give four examples of magnetic materials?

Answer 7

Iron, steel, cobalt, nickel

Question 8

How does the strength of a magnetic field as you move further away from the magnet?

Answer 8

The strength decreases

Question 9

In what direction does a magnetic field point?

Answer 9

From the North Pole to the south

Question 10

What does a magnetic compass contain?

Answer 10

A small bar magnet that points in the direction of the Earth’s magnetic field

Question 11

What is produced when current flows through a conducting wire?

Answer 11

A magnetic field is produced around the wire

Question 12

What determines the strength of the magnetic field around a current-varying wire?

Answer 12

The magnitude of the current flowing through the wire

Question 13

What does a high concentration of field lines mean?

Answer 13

The field is strong

Question 14

How is a plotting compass used to map out a magnetic field?

Answer 14

Place the compass of a piece of paper, draw an arrow in the direction the compass points. Repeat at different points on the paper. Join the arrows and make a complete field pattern

Question 15

What is a solenoid?

Answer 15

A could of wire which creates a strong magnetic field when current passes through it.

Question 16

Describe the magnetic field inside a solenoid

Answer 16

Strong and uniform

Question 17

Is the field on the outside of a solenoid strong or weak? Why?

Answer 17

Weak because the fields from each coil cancel out, making the outside field weak

Question 18

What is an electromagnet?

Answer 18

A solenoid with an added iron core.

Question 19

What is the motor effect?

Answer 19

When a force is exerted between a magnetic field and a current-carrying conductor placed in that field

Question 20

What rule is used to determine the force produced by the motor effect?

Answer 20

Fleming’s left-hand rule

Question 21

What do each of the fingers represent in fleming’s left hand rule?

Answer 21

The forefinger = magnetic field
Second finger = current flow
Thumb = direction of force produced by motor effect

Question 22

What factors affect the size of the force on a current-carrying wire in a magnetic field?

Answer 22

The magnitude of the current flowing through the conductor

The strength of the magnetic field that the conductor is placed in

Question 23

If the direction of current in a current-carrying wire placed in a uniform magnetic field is reversed, what happens to the force?

Answer 23

The direction of the force is reversed

Question 24

If the strength of the current in a current-carrying wire placed in a a uniform magnetic field is increased, what happens to the force?

Answer 24

The strength of the force is increased

Question 25

How do you calculate force? (magnetic flux)

Answer 25

Force = magnetic flux density x current x length

Question 26

What criteria must be met for the equation linking force, magnetic flux density , current and length to hold?

Answer 26

The conductor must be at right angles to the magnetic field it is placed in

Question 27

What unit is used for magnetic flux density?

Answer 27

Tesla

Question 28

If the current and the magnetic field are parallel to each other, which direction would the force act in?

Answer 28

No force will act

Question 29

How does al electric motor work?

Answer 29

A coil of wire is placed in a magnetic field
The forces on the two sides perpendicular to the field experience forces in opposite directions. This causes a rotational effect

Question 30

How are electric motors kept rotating?

Answer 30

A split ring commutator is used. This switches the current direction every half turn, which ensures that the coil keeps spinning