topic 12 - magnetism and the motor effect

Question 1

like poles

Answer 1

repel

Question 2

unlike poles

Answer 2

attract

Question 3

what are the 3 main magnetic materials

Answer 3

iron
cobalt
nickel
(some alloys and compounds of these metals are also magnetic)

Question 4

what is the magnetic force between a magnet and magnetic material

Answer 4

always attractive (due to magnetic induction)

Question 5

permanent magnet

Answer 5

magnets that produce their own magnetic field all of the time

Question 6

induced/temporary megnats

Answer 6

only produce a magnetic field when they are IN another magnetic field
made by placing any magnetic material inside a magnetic field
once the field is removed, they lose their magnetism

Question 7

magnetically soft (material example and meaning)

Answer 7

pure iron and nickel-iron alloys

lose magnetism very quickly

Question 8

magnetically hard (material example and meaning)

Answer 8

steel

lose magnetism more slowly - used to make permanent magnets

Question 9

magnetic field

Answer 9

the region around a magnet where other magnets or magnetic materials experience a force

Question 10

field lines flow in what direction

Answer 10

north -> south

Question 11

field lines show

Answer 11

which way a force would act on a north pole at that point in the field

Question 12

where are the magnetic field and magnetic forces the strongest

Answer 12

at the poles

Question 13

uniform magnetic field

Answer 13

a magnetic field where the field is the same strength everywhere

Question 14

how can you investigate magnetic field of an object using plotting compasses (5)

Answer 14

1) place magnet on a piece of paper, draw around it
2) place the compass on the paper near the magnet - the needle will point in the direction of the field line in this position
3) mark direction of compass needle with two dots
4) move compass so that the tail end is where the tip is where it was in the previous position ; put a dot at the new tip
5) repeat and join up the dots to have one drawing of a field line around the magnet
6) repeat at different points around the magnet to get several field lines

Question 15

compass

Answer 15

an object containing a needles that always lines up with the magnetic field it is in

Question 16

why do compasses point north and how do we know our earth’s core is magnetic

Answer 16

the earth generates its own magnetic field
compasses point to follow the field lines from north to south
our geographical north is our magnetic south pole
this shows that the Earth’s core must be magnetic

Question 17

what happens when a current flows through a long straight conductor

Answer 17

a magnetic field is created around it

the field consists of concentric circles around and perpendicular to the wire

Question 18

right hand thumb rule (method)

Answer 18

point thumb in current direction and curl fingers

Question 19

what does the right hand thumb rule tell you

Answer 19

the direction of the magnetic field

Question 20

how can you increase the strength of the field around a long straight conductor (2)

Answer 20

• increase the size of the current

- go closer to the wire

Question 21

where is the force on the wire strongest (motor effect)

Answer 21

when the wire is at 90° to the magnetic field

Question 22

what happens if the wire runs along the field (motor effect)

Answer 22

no force is experienced at all

Question 23

what does a ● or ✖ mean in diagrams about a wire

Answer 23

● means that the wire is coming towards you

✖ means that the wire is going away from you

Question 24

motor effect

Answer 24

when a current-carrying conductor is place between magnetic poles, the two magnetic field interact to produce a force on the wire

Question 25

the force from the motor effect always acts in the same direction relative to what

Answer 25

the magnetic field and the current direction of the wire

Question 26

what does each finger in Fleming’s left hand rule indicate

Answer 26

First finger - Field
seCond finger - Current
thuMb - force/ Motion

Question 27

size of force (motor effect) formula

Answer 27

force = magnetic flux density x current x length

Question 28

what is magnetic flux density and what is it measured in

Answer 28

number of field lines in a given region

Tesla (T) or newtons per ampere per metre (N/Am

Question 29

what situation does the size of force (motor effect) formula apply to

Answer 29

when the current is at 90° to the magnetic field it is in

Question 30

how does a d.c MOTOR work

Answer 30

forces act on either side of a coil/wire carrying a current
these forces act in opposite directions on either side so the coil rotates
the split ring commutator swaps the contacts every half turn to keep the wire spinning
the direction of the motor can be reverse by swapping polarity or swapping poles over

Question 31

solenoid

Answer 31

a long coil of wire

Question 32

how can you increase the magnetic field strength of a single piece of wire

Answer 32

wrap it in a long coil with lots of loops

Question 33

electromagnet + example

Answer 33

a magnet that can be turned on and off using electric current
eg. solenoid

Question 34

what is the field like between individual wires in a solenoid

Answer 34

the field lines cancel each other out so the field is very weak apart from at solenoid ends

Question 35

what is the field like inside the solenoid loops

Answer 35

the field lines add together to form a stronger and almost uniform field

Question 36

what does direction of field in a solenoid depend on

Answer 36

direction of current

Question 37

how can you increase the magnetic field strength of a solenoid and why

Answer 37

by putting a block of iron in the centre of the coil

this becomes an induced magnet whenever current is flowing