Magnetism and Electromagnetism

Question 1

what do magnets do?

Answer 1

repel and attract other magnets and attract other magnetic materials

Question 2

what are non-magnetic materials?

Answer 2

materials that are not attracted to magnets and cannot be magnetised

Question 3

what are examples of non-magnetic materials?

Answer 3

• glass
• plastic

Question 4

what are magnetic materials?

Answer 4

materials that are attracted to magnets and can be magnetised

Question 5

what are examples of magnetic materials?

Answer 5

• iron
• steel
• nickel
• cobalt

Question 6

how can magnetism be induced in magnetic materials?

Answer 6

by placing them in a magnetic field

Question 7

what is an example of
a magnetically hard material?

Answer 7

steel

Question 8

what are magnetically soft materials?

Answer 8

magnetic materials that are only temporarily soft

Question 9

what are magnetically hard materials?

Answer 9

magnetic materials that can be permanently magnetised

Question 10

what is an example of a magnetically soft material?

Answer 10

soft iron

Question 11

what do magnetic field lines represent?

Answer 11

the magnetic force on a north pole at a given point

Question 12

what does the direction of a magnetic field line show?

Answer 12

the direction of the force

Question 13

what does the distance between the magnetic field lines show?

Answer 13

the magnitude of the force

Question 14

what direction do magnetic field lines point?

Answer 14

from north to south

Question 15

what does a uniform magnetic field look like?

Answer 15

the field lines are parallel and evenly spaced

Question 16

what does an electric current passing through a conductor produce?

Answer 16

a magnetic field around it

Question 17

what do electromagnets consist of?

Answer 17

a coil of wire wrapped around a magnetically soft core and can be turn on and off

Question 18

what is the motor effect?

Answer 18

a force acts on a current-carrying conductor in a magnetic field - Fleming’s left hand rule shows the relative directions of the force, field and current

Question 19

if the current is reversed or the magnetic field is reversed…

Answer 19

the force will be reversed

Question 20

if the magnitude of the current or of the magnetic field is increased…

Answer 20

the magnitude of the force will increase

Question 21

what do DC motors consist of?

Answer 21

a coil of wire in between two permanent magnets

Question 22

how do DC motors work?

Answer 22

• direct current flows through the wire and it experiences a turning effect due to the forces exerted on it in the magnetic field
• as the current flows in opposite directions on each side of the coil, the forces on each side are in opposite directions, making it turn

Question 23

how can the turning effect in DC motors be increased?

Answer 23

• by increasing the current
• by using a stronger magnetic field
• by increasing the number of turns on the coil

Question 24

what is a split ring commutator used for?

Answer 24

to ensure that the direction that the current flows in the coil reverses every half turn

Question 25

what do loud speakers consist of?

Answer 25

a coil attached to a cone in a magnetic field

Question 26

how do loud speakers work?

Answer 26

- when alternating current flows through the coil, the cone is continuously pushed away and pulled back, making a sound - the frequency of the sound can be altered by changing the frequency of the alternating current used

Question 27

why is a force exerted on charged particles in a magnetic field?

Answer 27

because moving charged particles are current as long as they are not moving parallel to the field

Question 28

what is the generator effect?

Answer 28

- when there is a relative movement between conducting wire and a magnetic field, a voltage will be induced - for example, if conducting wire moves across a magnetic field, a voltage will be induced in it - if it is part of a complete circuit, this causes a current to flow

Question 29

how can induced voltage be increased in electromagnetic induction?

Answer 29

- by moving the wire more quickly - using a stronger magnetic field - increasing the length of the wire inside the magnetic field

Question 30

can a voltage be induced in a coil with a changing magnetic field through it?

Answer 30

yes - for example, when a magnet is moved into a coil, a voltage is induced in it

Question 31

the more quickly the magnetic field changes...

Answer 31

the greater the voltage

Question 32

how can electricity be generated?

Answer 32

- by rotating a magnet within a coil or by rotating a coil in a magnetic field - as they rotate, the magnetic field through the coil changes, which induces a voltage and therefore a current in the coil

Question 33

how can voltage be increased when generating electricity?

Answer 33

- by increasing the length of wire inside the magnetic field - by using a stronger magnet - by increasing the speed of rotation

Question 34

what does a transformer consist of?

Answer 34

two coils wrapped around a soft iron core and is used to change the size of a voltage?

Question 35

what are transformers used for?

Answer 35

- to step up the voltage (to a greater value) for transmission in power lines which reduces power loss (because lower current causes less power loss due to the resistance of the cables) - then step down the voltage for usage in homes (to keep us safe)

Question 36

what does an alternating voltage produce in the primary coil?

Answer 36

an alternating current - this creates a changing magnetic field which links with the secondary coil and induces an alternating voltage in it

Question 37

a step-up transformer has more turns on the secondary than the primary which means...

Answer 37

the voltage of the secondary is greater than that of the primary

Question 38

a step-down transformer has fewer turns on the secondary than the primary which means...

Answer 38

the voltage of the secondary is less than that of the primary