TOPIC 7 FINAL

Question 1

A magnetic has what?

Answer 1

A north and south pole.

Question 2

What do all magnets produce?

Answer 2

A magnetic field

Question 3

When two like poles meet what happens?

Answer 3

A force of repulsion

Question 4

When two opposite poles meet what happens?

Answer 4

A force of attraction

Question 5

Magnetic forces are always what?

Answer 5

A non-contact force

Question 6

What is a magnetic field?

Answer 6

An area around an object where it experiences a magnetic force.

Question 7

What can you use to show the direction of a Magnetic field?

Answer 7

A compass

Question 8

What is in a Compass?

Answer 8

A tiny bar magnet.

Question 9

In a compass the North pole is always attracted to what?

Answer 9

The south pole, so the compass points in the direction of the magnetic field.

Question 10

How do you know in a magnetic field where it is strongest?

Answer 10

Where the lines are close together near the poles of the bar magnet.

Question 11

Where is the magnetic field weakest at?

Answer 11

When the lines are not close together.

Question 12

The earth has what?

Answer 12

A magnetic field

Question 13

On a compass where would north point to on the earth’s magnetic field?

Answer 13

It will point to earth’s magnetic south

Question 14

What is a Permanent Magnet?

Answer 14

They produce their own magnetic field and only experience a force of attraction and repulsion.

Question 15

What is an Induced Magnet?

Answer 15

Are magnetic materials that turn into a magnets when they are placed in a magnetic field.

Question 16

If a magnet is induced what does it mean?

Answer 16

It will only ever be Attracted to a permanent magnet.

Question 17

Name the 4 magnetic materials

Answer 17

Iron
Steel
Cobalt
Nickel

Question 18

In a Series circuit if the switch is open what does it mean?

Answer 18

Their is no current which means their is no magnetic field around the wire

Question 19

In a Series circuit if Switch is closed what does that mean?

Answer 19

It means Direct current can flow producing a magnetic field around the whole wire

Question 20

What does the strength of the magnetic field through a wire depend on?

Answer 20

Size of the current. A larger current produces a larger magnetic field.

Question 21

Where else is the magnetic field strongest at in a current carrying wire?

Answer 21

It is strongest closer to the wire, as we move further away from wire, the strength of magnetic field decreases.

Question 22

if we change the direction of the current in a current carrying wire in a closed circuit what does this mean?

Answer 22

We change the direction of the magnetic field.

Question 23

How do we work out the direction of the magnetic field produced by a wire?

Answer 23

We use the right hand grip rule. Using your right hand, point your thumb in the direction of current and curl your fingers. The direction of your fingers is the direction of the field.

Question 24

What is a final way to increase the strength of the magnetic field that a wire produces.

Answer 24

Wrapping wire into a coil called a solenoid.

Question 25

What happens when we use a solenoid in a current carrying wire?

Answer 25

When we turn on current we get a strong and uniform magnetic field, inside the solenoid.

Question 26

What is similar about the magnetic field of a bar magnet and the magnetic field around solenoid?

Answer 26

It has the same magnetic field around it.

Question 27

What can you use to work out what end is north pole and what end is south pole of a solenoid?

Answer 27

By using the right hand grip rule.

Question 28

What are the 3 ways to increase the magnetic field produced by a solenoid?

Answer 28

1) Increase the current, strengthening the magnetic field 2) Increase the number of coils to increase magnetic field. 3) Place an iron core inside the solenoid increasing the strength of the magnetic field.

Question 29

Why would you place an iron core in the center of the solenoid?

Answer 29

Because it is an induced magnet when current is flowing.

Question 30

What is a Electromagnet?

Answer 30

A solenoid containing a iron core.

Question 31

What makes Electromagnets useful?

Answer 31

We can turn on and off the electromagnet and also we can change the strength of the magnetic field.

Question 32

What is Direct current?

Answer 32

In a circuit the current from the cell only moves in one direction

Question 33

What is the Motor effect?

Answer 33

When a current carrying a wire will experience a force when placed in a Magnetic field because the Magnetic field interacts with magnetic field of the magnet.

Question 34

How do you calculate size of force acting on a conductor in a magnetic field?

Answer 34

Force (N) = B (magnetic flux density, Tesla) X I (current Amps) X L (length of conductor in M)

Question 35

What does the question only apply to?

Answer 35

It only applies to a wire which is at right angles to the magnetic field. It will not experience a force at all if in parallel.

Question 36

What are the 3 factors that affect size of the force?

Answer 36

1) The magnetic flux density 2) Current 3) Length of conductor

Question 37

A 35 cm long piece of wire is at 90% to the external magnetic field. The wire experiences a force of 9.8 N when a current of 5.0 A is flowing through it. Calculate the magnetic flux density of the field?

Answer 37

35 cm = 0.35m b = F /I X L 9.8 / (5.0 X 0.35) = 5.6T

Question 38

What can you use to find the direction of the force?

Answer 38

Fleming's left hand rule.

Question 39

How do you use Fleming's left hand rule?

Answer 39

1) Place first finger in the direction of the magnetic field. (N to S) 2) Now point your second finger in the direction of the current (+ to -) 3) The direction that your thumb is pointing, shows you the direction of the force.

Question 40

What is a useful application of the Motor effect?

Answer 40

Electric motors

Question 41

What can you use to find the direction of the force in an electric motor?

Answer 41

Using Fleming's left hand rule.

Question 42

What is the problem of Electric motors?

Answer 42

The loop rotates at 90', this is a problem as once the loop is at 90', it will stop rotating.

Question 43

What is a split ring commutator?

Answer 43

It is a clever way of swapping the contacts every half turn to keep the motor from rotating in the same direction.

Question 44

How can the direction of the electric motor be reversed?

Answer 44

1) Swapping the polarity of the dc supply ( reversing the current) 2) Swapping the magnetic poles over (reversing the field)

Question 45

What are the 3 ways to increase the speed of the electric motor be increased?

Answer 45

1) Increasing the current 2) Adding more turns to the coil 3) increasing the magnetic flux density