Magnetism

Question 1

What is electromagnetic induction?

Answer 1

The creation of a voltage (and maybe current) in a wire due to a change in magnetic field.

Question 2

What is the generator effect?

Answer 2

When you move a wire in a magnetic field to produce a current. Or… When a magnet moves around a wire to produce a current.

Question 3

How can I increase the voltage I get out of a dynamo/generator?

Answer 3

Increase the number of turns in the coil Increase the strength of the magnet Move the wire/magnet faster Reduce the gap between the wire and the magnet

Question 4

How can I increase the current I get out of a generator?

Answer 4

Increase the number of turns in the coil Increase the strength of the magnet Move the wire/magnet faster Reduce the gap between the wire and the magnet

Question 5

What is the energy transfer that occurs in a generator?

Answer 5

Kinetic energy -> Electrical energy

Question 6

If I reverse the direction of the movement of a wire in a magnetic field, what happens to the current?

Answer 6

The current/voltage reverses too.

Question 7

How does electromagnetic induction work?

Answer 7

When the coil/wire cuts the magnetic field lines… …a voltage is induced… …by electromagnetic induction

Question 8

When I rotate a coil in a dynamo, at what part of the rotation is the biggest current/voltage induced?

Answer 8

When the coil is parallel to the magnetic field (because that’s when it cuts the most magnetic field lines)

Question 9

Other than generating electricity, what are some uses for electromagnetic induction?

Answer 9

Detecting metal pipes and wires in walls.

Question 10

As a generator coil turns around, where is the maximum voltage produced?

Answer 10

When the coil is perpendicular to the magnetic field

Question 11

As a generator coil turns around, where is the minimum voltage produced?

Answer 11

When the coil is parallel to the magnetic field

Question 12

If I move a wire in a magnetic field in a direction parallel to the magnetic field lines, why is no voltage produced?

Answer 12

No field lines are being cut by the wire.

Question 13

How does electricity generation in a power station work, generally?

Answer 13

Boil some water, use it to rotate a coil in a magnetic field.

Question 14

For most electricity generation, what type of current is produced?

Answer 14

AC

Question 15

If I reverse the polarity of the magnets used in a generator, what happens to the current I induce?

Answer 15

It reverses.

Question 16

If I reverse the magnets and the direction I rotate a generator coil, what happens to the current?

Answer 16

Nothing. It reverses twice, so it ends up the same.

Question 17

What does a split ring commutator do in a DC motor?

Answer 17

Reverses the direction of the current every half term

Question 18

How does a motor work?

Answer 18

• The current produces a magnetic field - This field interacts with the permenant field - Producing a force which turns the motor

Question 19

What does each finger correspond to in Fleming’s Left Hand Rule?

Answer 19

Thumb = Force (F) Index = Magentic Field (B) Middle = Current (I)

Question 20

How do I tell the strength of a magnetic field from its field lines?

Answer 20

The closer together they are, the bigger the magnetic field.

Question 21

What is shown by the direction a field line points?

Answer 21

The direction the north pole of a compass would point when placed in the field.

Question 22

When does a current carrying wire NOT produce a force in a magnetic field?

Answer 22

When the current is PARALLEL to the magnetic field

Question 23

What is the wire in a motor made of and why?

Answer 23

Copper, because it’s a good conductor

Question 24

What are the brushes on a DC motor made of

Answer 24

Carbon, because it’s a conductor and its hard wearing

Question 25

What is a uniform field?

Answer 25

One where the field lines are parallel and evenly spaced

Question 26

What direction do magnetic field lines always point?

Answer 26

From North to South

Question 27

What is the motor effect?

Answer 27

When a current carrying wire is in a magnetic field, a force is produced.

Question 28

Why does a current carrying wire in a magnetic field move?

Answer 28

• The current produces a magnetic field - This field interacts with the permenant field - Producing a force

Question 29

Why do the coils of an electromagnet have to be insulated?

Answer 29

Otherwise the coils will short circuit and the current will not flow through the coils.

Question 30

How does a loudspeaker work?

Answer 30

• The current produces a magnetic field - This field interacts with the permenant field - Producing a force which moves the cone

Question 31

How do I set up a uniform magnetic field?

Answer 31

Two bar magnets with opposite poles close together, facing one another.

Question 32

Describe an experiment I can do to see the magnetic field around a magnet?

Answer 32

• Place the magnet on a piece of paper
• Place a plotting compass at the end of a magnet
• Place an “x” at the point the compass points to.
• Place the compass so that the back end of the arrow touches the “x”. Place another “x” where the arrow is pointing.
• Repeat until you leave the page or you meet the magnet again
• Repeat the entire process again, starting at a different point.