Magnetism

Question 1

What will two north poles do to each other?

Answer 1

Repel

Question 2

What will two south poles do to each other?

Answer 2

Repel

Question 3

What will a south and north pole do to each other?

Answer 3

Attract

Question 4

Is mangentism an example of a contact or non contact force?

Answer 4

Non contact

Question 5

State some differences between permanent and induced magnets

Answer 5

A permanent magnet always has a magnetic field. An induced magnet only becomes magnetic when placed in a magnetic field.
Induced magnets always causes force of attraction.
Permanent magnets can attract or repel

Question 6

State the magnetic materials

Answer 6

Iron, steel, cobalt, nickel

Question 7

What do we call the region around a magnet where a force acts on another magnetic material?

Answer 7

Magnetic field

Question 8

What is the relationship between the size of attraction/repulsion and distance from a magnet

Answer 8

As distance increase the force or field gets weaker

Question 9

Where is the strength of a magnetic field the strongest?

Answer 9

The poles of a magnet

Question 10

Why do magnetic field lines always need arrows on them?

Answer 10

The direction of the magnetic field at any point is given by the direction of the force that would act on another north pole placed
at that point. The direction of a magnetic field line is from the north (seeking) pole of a magnet to the south(seeking) pole of the magnet.

Question 11

Describe how a magnetic compass works

Answer 11

A magnetic compass contains a small bar magnet. The Earth has a magnetic field. The compass needle points in the direction of the Earth’s magnetic field.

Question 12

Describe how a magnetic compass can be used to find the pattern around a bar magnet.

Answer 12

Put the magnet in the middle of the piece of paper and draw around it.
Draw nine dots around the north end of the magnet.
Put a plotting compass on the paper so that its tail is over one of the dots.
Draw a dot on the paper near to the point of the compass.
Join the two dots and mark the line with an arrow.
Then move the compass so that its tail is over your new dot.
Make another dot next to the point.
Repeat until you come to the edge of the paper or loop back round to the south pole.

Question 13

When a current flows what is always created?

Answer 13

A magnetic field

Question 14

What factors affect the strength of the magnetic field produced by a current?

Answer 14

1. Size of the current

2. Distance from the wire

Question 15

What is a solenoid?

Answer 15

When a current carrying wire is turned into a coil. this will increase the strength of the magnetic field.

Question 16

Describe the magnetic field inside a solenoid

Answer 16

The magnetic field inside a solenoid is strong and uniform.

Question 17

Describe the magnetic field around a solenoid

Answer 17

The magnetic field around a solenoid has a similar shape to that of a bar magnet.

Question 18

How can a solenoid be turned into an electromagnet?

Answer 18

Adding an iron core, this again increases the strength of the magnetic field.

Question 19

Describe the magnetic field of an electromagnet

Answer 19

Its the same as a bar magnet

Question 20

How can the strength of an electromagnet be increased?

Answer 20

Larger current
More turns
Using an iron core

Question 21

Describe the magnetic field produced by a straight wire carrying a current

Answer 21

circular rings around the wire. the right hand rule shows the direction of the magnetic field

Question 22

Describe the right hand rule for a straight wire carrying a current

Answer 22

Thumb points in the direction of the current, fingers curl around in the direction of the magnetic field

Question 23

What is the motor effect?

Answer 23

When a conductor carrying a current is placed in a permanet magnetic field the magnet producing the field and the conductor exert a force on each other.

Question 24

Describe Fleming’s left hand rule.

Answer 24

Thumb, first finger and second finger are put at right angles to each other.
Thumb - direction of force/motion
First Finger - direction of magnetic field (always from North to south)
seCond finger - direction of current (always from positive to negative)

Question 25

In the motor effect how can the size of the force be increased?

Answer 25

Larger current
Stronger permanent magnets
Longer length of wire inside the magnetic field
Keeping the conductor at a right angle to the magnetic field

Question 26

In the motor effect how can the direction of the force be reversed?

Answer 26

Reversing the direction of the current

Reversing the poles of the permanent magnets

Question 27

State the units for magnetic flux density.

Answer 27

Tesla (T)

Question 28

Describe how a coil of wire inside a magnetic field can cause rotation eg an electric motor

Answer 28

The current goes into the coil of wire, creating an electromagnetic field. This interacts with a the permanent magnetic field causing a force of attraction or repulsion.
the current then comes out of the coil changing direction so the force changes direction. This causes rotation.

Question 29

How do loudspeakers/headphones use the motor effect to create sound waves.

Answer 29

A coil of wire is wrapped around a permanent magnet. An alternating current passes through the wire creating an electromagnetic field. the magnetic field from the current and permanent magnetic interact causing a force of attraction or repulsion. As the current is a.c. the force changes between attraction and repulsion. This causes the loud speaker cone to vibrate which creates sound waves.