Magnetism

Question 1

where are the magnetic forces are strongest?

Answer 1

at the poles of the magnet

Question 2

what do like poles do?

Answer 2

repel

Question 3

what do unlike poles do?

Answer 3

attract

Question 4

what is attraction and repulsion?

Answer 4

a non-contact force

Question 5

what is an induced magnet?

Answer 5

An induced magnet is a material that becomes a magnet when it is placed in a magnetic field.

When removed from the magnetic field an induced
magnet loses most/all of its magnetism quickly.

Question 6

name the magnetic materials

Answer 6

cobalt, nickel, steel, iron

Question 7

what is an electromagnet?

Answer 7

An electromagnet is a solenoid with an iron core.

Question 8

what force do induced magnets create

Answer 8

attraction force (with the permanent magnet)
 - as the poles of the induced magnetic will be the reverse of those of the permanent magnet

Question 9

what is a magnetic field?

Answer 9

The region around a magnet where a force acts on another magnet or on a magnetic material (iron, steel, cobalt and nickel)

Question 10

what does the strength of the magnetic field depends on?

Answer 10

distance from the magnet.

Question 11

what is the direction of the magnetic field at any point?

Answer 11

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.

Question 12

in which direction do field lines go?

Answer 12

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 13

how does a compass work?

Answer 13

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 14

describe the motor effect

Answer 14

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

Question 15

what happens when a current flows through a conducting wire?

Answer 15

a magnetic field is produced around the wire

Question 16

what does the magnetic field strength around a wire depend on?

Answer 16

on the current through the wire and

the distance from the wire.

Question 17

why do solenoids have the wire in coils?

Answer 17

increases the strength of the magnetic field created by a current through the wire

Question 18

magnetic field inside a solenoid is…

Answer 18

strong and uniform

Question 19

why have an iron core in a solenoid?

Answer 19

Adding an iron core increases the strength of the

magnetic field of a solenoid

Question 20

describe the magnetic field outside a solenoid

Answer 20

has a similar shape to that of a bar magnet

Question 21

what is the equation linked to Flemming’s left hand rule?

Answer 21

F = I x B x L
force = current x length of wire x magnetic flux density

Question 22

what does each finger represent in Flemming’s left hand rule?

Answer 22

thuMb = Motion
First Finger = magnetic Field
seCond finger = Current

Question 23

describe the basis of the electric motor

Answer 23

A coil of wire carrying a current in a magnetic field tends to rotate

Question 24

name the uses of the motor effect

Answer 24

loudspeakers and headphones

Question 25

what do loudspeakers and headphones do?

Answer 25

use the motor effect to convert variations in current in electrical circuits to the pressure variations in sound waves.

Question 26

how do you increase the force acting on the coil (motor effect)?

Answer 26

increase number of coils increase current increase magnetic field strength

Question 27

explain how loudspeakers work

Answer 27

has an electromagnet inside a coil - the changing current causes a changing the induced magnetic field in the electromagnet - a stationary magnet continuously attracts and repels the electromagnet - this causes the speakers to move back and forwards - this creates sound waves

Question 28

what is the generator effect?

Answer 28

If an electrical conductor moves relative to a magnetic field or if there is a change in the magnetic field around a conductor, a potential difference is induced across the ends of the conductor. If the conductor is part of a complete circuit, a current is induced in the conductor

Question 29

what does an induced current generate?

Answer 29

a magnetic field that opposes the original change, either the movement of the conductor or the change in magnetic field.

Question 30

what factors that affect the size of the induced potential difference/induced current?

Answer 30

- amount turns in the coil of wire | - speed of movement

Question 31

what factors that affect the direction | of the induced potential difference/induced current?

Answer 31

- direction of the magnetic field | - direction of the current

Question 32

define D.C. current

Answer 32

direct current - flows in only one direction - used for phones and batteries

Question 33

define A.C. current

Answer 33

alternating current - flows in both direction (oscillates) - used for the mains

Question 34

how do Alternating Current Generators work?

Answer 34

as the coil (or magnet) spin, a current in induced in the coil, this changes direction every half turn ac generators have slip rings and brushes so the contacts don't swap every half turn therefore they produce and alternating current

Question 35

how do Dynamos work?

Answer 35

as the coil (or magnet) spins, a current is induced in the coil dynamos have a split ring communicator (instead of slip rings) this swaps the connection every half turn so the current flows in the same direction thus is creates direct current

Question 36

how does an electric motor work?

Answer 36

forces act on the two arms of the coil of wire that is carrying current coil is on a spindle, one force acts upwards, the other downwards, it rotates split-ring communicator is a way of swapping the contacts every turn to keep the motor rotating in the same direction

Question 37

Microphones use the generator effect to...

Answer 37

convert the pressure variations in sound waves into variations in current in electrical circuits.

Question 38

how does a moving-coil microphone | work?

Answer 38

sound waves hit the flexible diaphragm that is attached to a coil of wire, wrapped around a magnet. - this causes the coil of wire to move in the magnetic field, which generates current - ( the movement of the coil depends on the sound wave) - thus convert sound waves into electrical currents

Question 39

what does a basic transformer have?

Answer 39

A basic transformer consists of a primary coil and a secondary coil wound on an iron core (iron is used as it is easily magnetised.)

Question 40

step-up transformer

Answer 40

more turns in the secondary coil than primary

Question 41

step-down transformer

Answer 41

more turns in the primary coil than secondary

Question 42

what do transformers do?

Answer 42

increase (step-up) or decrease (step-down) voltage (for safety and travel)

Question 43

how does a transformer work?

Answer 43

1) when an alternating p.d. is applied across the primary coil, the iron core magnetises and demagnetises quickly, 2) this changing megnetic field induces an alternating p.d. in the secondary coil, 3) if the secondary coil is part of a circuit, this causes a current to be induced

Question 44

state the equation linked to transformers

Answer 44

input/ output = number primary coils/ number of secondary coils p.d. x current (primary coil) = p.d. x current (secondary coil)

Question 45

uses of transformers, and their importance

Answer 45

low current/high p.d. means less energy is wasted heating the wires, so increasing p.d. make the national grid more efficient in transporting electricity across the nation

Question 46

describe how an electromagnet is used in a circuit breaker

Answer 46

circuit contains an electromagnet and a switch | - when a large current flows, the electromagnet attracts the switch - this turns the circuit ofd

Question 47

describe how an electromagnet is used in an electric bell

Answer 47

when a switch is pressed, an electromagnet attracts the iron bar which hits the bell - the movement of the bar also breaks the circuit, turing the electromagnet off and returning the bar to its original position - the process repeats quickly

Question 48

describe how an electromagnet is used in a relay switch

Answer 48

- a low voltage circuit is turned on, activating an electromagnet - the electromagnet attracts the iron switch, turning on a second, high voltage circuit