Topic 12 - Magnetism And The Motor Effect

Question 1

What is an electromagnet?

Answer 1

• A solenoid with an added iron core
• Adding the iron core increases the strength of the magnetic field

Question 2

What is the motor effect?

Answer 2

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

Question 3

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

Answer 3

Fleming’s Left-Hand Rule

Question 4

First finger Flemings LH Rule:

Answer 4

Magnetic field

Question 5

Second Finger Flemings LH Rule

Answer 5

Current Flow

Question 6

Thumb Flemings LH Rule

Answer 6

Direction of the force

Question 7

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

Answer 7

• The magnitude of the current flowing through the conductor
• The strength of the magnetic field that the conductor is placed in

Question 8

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

Answer 8

• Direction of the force is reversed

Question 9

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

Answer 9

The strength of the force is increased.

Question 10

Equation linking force, magnetic flux density, current and length.

Answer 10

Force (N) = Magnetic Flux Density (T) x Current (A) x Length (m)

F = BIL

Question 11

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

Answer 11

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

Question 12

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

Answer 12

No force will act

Question 13

How does an electric motor work?

Answer 13

• A coil of wire, carrying a current, 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 14

How are electric motors kept rotating?

Answer 14

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

Question 15

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

Answer 15

The poles

Question 16

What happens when two magnets are brought close to each other?

Answer 16

They exert a force on each other

Question 17

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

Answer 17

• A repulsive, non-contact force.

Question 18

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

Answer 18

An attractive, non-contact force.

Question 19

What is a magnetic field?

Answer 19

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

Question 20

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

Answer 20

• Permanent magnet produces its own magnetic field.
• Induced magnet becomes magnetic when placed in a magnetic field

Question 21

Induced magnetism always causes what type of force?

Answer 21

Force of attraction.

Question 22

What is the effect when an induced magnet is removed from a magnetic field?

Answer 22

The induced magnet loses most/all of its magnetism.

Question 23

Four examples of magnetic materials:

Answer 23

• Iron
• Steel
• Cobalt
• Nickel

Question 24

What can always be said about the force between a magnet and a magnetic material?

Answer 24

It is always attractive

Question 25

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

Answer 25

The magnetic field strength decreases the further you move away,

Question 26

In what direction does a magnetic field point?

Answer 26

• In the direction of the force that a North Pole would experience if placed in the field.
• From the north seeking pole to the south seeking pole of a magnet.

Question 27

What does a magnetic compass contain?

Answer 27

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

Question 28

What is produced when current flows through a conducting wire?

Answer 28

A magnetic field is produced around the wire.

Question 29

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

Answer 29

The magnitude of the current flowing through the wire.

Question 30

Does a high concentration of field lines mean the field is strong or weak?

Answer 30

Strong

Question 31

Do magnetic field lines ever cross each other?

Answer 31

No, they never cross, touch or overlap

Question 32

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

Answer 32

• Place a compass (with a needle magnet) on a piece of paper near the field.
• Draw an arrow in the direction the compass points.
• Repeat at different points on the paper.
• Join the arrows to make a complete field pattern.

Question 33

What is a solenoid?

Answer 33

• A coil of wire which when current passes through creates a strong magnetic field

Question 34

Describe the magnetic field found inside a solenoid

Answer 34

Strong and uniform

Question 35

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

Answer 35

• Weak
• This is because the fields from each coil cancel out, making the outside field weak.