Magnetism, the motor effect, and electromagnetic induction

Question 1

A bar magnet is an example of a _________ magnet.

Answer 1

Permanent

Question 2

When a piece of magnetic material is in a magnetic field it becomes a magnet itself e.g. when one paperclip attracts the next paperclip. This is called an ________ magnet.

Answer 2

Induced

Question 3

List the three magnetic elements.

Answer 3

Iron, nickel and cobalt

Question 4

What is a magnetic field?

Answer 4

The area around a magnet where it can attract magnetic materials

Question 5

Magnetic field lines never cross, and always include arrows that point from ____ to ____

Answer 5

North to South

Question 6

The shape of a magnetic field can be found using a:

Answer 6

Plotting compass

Question 7

What does it tell you if magnetic field lines are close together?

Answer 7

The field is strong

Question 8

Where are the field lines closest together around a bar magnet?

Answer 8

At the poles

Question 9

Describe the field lines in a uniform field

Answer 9

Parallel, equidistant, arrows pointing from N to S

Question 10

Which rule do you use to work out the direction of the magnetic field around a current carrying wire?

Answer 10

The right hand grip rule

Question 11

What kind of magnet is created when you pass a current through a coil of wire?

Answer 11

An electromagnet

Question 12

Describe the shape of the magnetic field around a solenoid

Answer 12

similar to that of a bar magnet, almost uniform and strong inside the coil, weaker above and below the coil

Question 13

How can you increase the strength of an electromagnet?

Answer 13

More Coils, larger Current, or use a magnetic Core e.g. Iron

Question 14

What do the thumb, fore finger and second finger represent in Flemming’s left hand rule?

Answer 14

Thumb = Force
fore finger = Magnetic Field
second finger = Current

Question 15

What is the equation that gives the strength of the force on a current carrying wire within a magnetic field?

Answer 15

F = B x I x L

Force(N) = Magnetic field strength (T) x Current (A) x length (m)

Question 16

What is the name of the effect that makes a wire ‘jump’ when it has a current passing through it and is placed within a magnetic field?

Answer 16

The motor effect

Question 17

What is the unit for Magnetic field strength (aka magnetic flux density)?

Answer 17

Tesla (T)

Question 18

What letter is used to represent magnetic flux density, or magnetic field strength?

Answer 18

B

Question 19

What does a step up transformer do to the voltage of an electricity supply?

Answer 19

Increases the voltage of an electricity supply

Question 20

What kind of current is needed for a transformer to work?

Answer 20

Alternating current

Question 21

In a step down transformer, where is there an induced voltage?

Answer 21

In all transformers there is an induced voltage in the secondary coil

Question 22

A step down transformer has (more/fewer) turns on the secondary coil compared to the primary coil

Answer 22

Fewer

Question 23

Calculate the missing value. Is this a step up or step down transformer? (VpIp = VsIs)
Vp = 500V
Ip = ?
Vs = 5V
Is = 2A

Answer 23

Step down.
Ip = 0.02A

Question 24

In order for energy to be conserved, what must always be the same in the primary and secondary coils of a transformer?

Answer 24

Power (or rate of energy transfer).

P = I V

Question 25

Where are transformers found in the national grid, and are they step up or step down transformers?

Answer 25

Step up transformers are used as the supply leaves the power station. Step down transformers are found just before the supply goes to factories, and again before the supply goes to homes.

Question 26

Why are transformers needed in the national grid?

Answer 26

Transformers are used to step up the voltage to 400kV in order to reduce the current. Lower current reduces energy dissipated through heat.

Question 27

How can you change the amount of potential difference induced?

Answer 27

Increase the number of turns in the coil, move the magnet faster or use a stronger magnet.

Question 28

How can you change the direction of an induced voltage?

Answer 28

Change the direction of motion or reverse the magnetic field.