p7 - magnetism

Question 1

how is an electromagnet made?

Answer 1

solenoid + iron core = electromagnet

Question 2

define an ‘ electromagnet ‘

Answer 2

a solenoid containing an iron core

Question 3

what happens when a current flows through a wire?

Answer 3

a magnetic field is produced around the wire

Question 4

what is a magnetic field?

Answer 4

an area surrounding a magnet that exerts a force on magnetic materials

Question 5

how can we prove / test for a magnetic field? [ rp ]

Answer 5

using a compass
when the current is off, the compass’ needle lines up with the Earth’s magnetic field

Question 6

what happens when a compass is placed next to a live current? and what does this mean?

Answer 6

deflects the compass = a magnetic field is present

Question 7

name the ways to increase the strength of a magnetic field:

Answer 7

increasing the size of the current
adding more turns to the coil
placing a piece of iron inside the solenoid

Question 8

define a solenoid

Answer 8

a coil of wire acting as a magnetic carrying electric current

Question 9

name some factors of a magnetic field:

Answer 9

stronger when closer to the wire
weaker when further away from the wire

change of direction in current= change of direction in magnetic field

closer the inducible metal to the magnet = stronger force

Question 10

what rule can we use to work out the direction of the magnetic field produced by a wire?

Answer 10

flemming’s right hand rule

Question 11

name the inducible metals

Answer 11

cobalt
iron
nickel
steel

Question 12

define inducible

Answer 12

can become a magnet

Question 13

what does a wire carry?

Answer 13

an electrical current

Question 14

when placing the wire into a magnetic field, what happens?

Answer 14

the magnetic field around the wire interacts with the magnetic field between the magnets

Question 15

what force does the wire in between the magnetic field create?

Answer 15

an upward force

Question 16

what does the upward force result in?

Answer 16

the wire moving upwards

Question 17

whats the formula to calculate the size of the force?

Answer 17

f = b x i x l

Question 18

define magnetic flux density

Answer 18

measures the strength of the magnetic field

Question 19

what does the ‘ size of a force’ formula apply to?

Answer 19

a wire which is at right angles to the magnetic field

Question 20

how can we determine the direction of the force?

Answer 20

flemming’s left hand rule

Question 21

what do the fingers mean in the left hand rule?

Answer 21

thumb : direction of the motion ( force )
first finger : direction of magnetic field ( from north to south )
second finger : direction of the conventional current ( + to - )

Question 22

using the left hand rule, why will it show that the direction of motion will be upwards?

Answer 22

the conductor is at right angles to the magnetic field

Question 23

what will happen if the conductor is parallel to the magnetic field?

Answer 23

the conductor will not experience a force

Question 24

what is the main application to the motor effect?

Answer 24

electric motors

Question 25

what wire do we use for an electric motor practical?

Answer 25

a loop of wire carrying a current, and the current is running back to front and front to back

Question 26

what happens when the loop of wire is placed into a magnetic field, and what does this result in?

Answer 26

the wire experiences a force on the left and right sides, which is a moment causing the loop to rotate in a clockwise direction

Question 27

what position is the loop rotated into?

Answer 27

90 o

Question 28

how can we solve the problem of the loop rotating?

Answer 28

switching the direction of the current when the loop passes 90 o

Question 29

how can we switch the direction of the current?

Answer 29

using a device called a split-ring commutator

Question 30

define a split-ring commutator

Answer 30

a split metal ring

Question 31

what is the split ring commutator connected to?

Answer 31

conducting brushes

Question 32

what do conducting brushes do?

Answer 32

allow the electric current to pass onto the ring

Question 33

what type of force does the current produce on the motor? and what does this result in?

Answer 33

a turning force, which makes the motor rotate in the clockwise direction

Question 34

what happens to the current once the motor has rotated? but what does the wire keep doing and why?

Answer 34

the current is broken for a fraction of a second, but the wire keeps turning due to momentum

Question 35

what can we summarise from the electric motor effect?

Answer 35

by switching the direction of the current, the split ring commutator allows the motor to keep rotating in the same direction

Question 36

what inducible material is used for transformers?

Answer 36

iron

Question 37

what does a step down transformer do?

Answer 37

increases the current
decreases the potential difference

Question 38

what does a step up transformer do?

Answer 38

increases the potential difference
decreases the current

Question 39

explain how a transformer works [ 3 ]

Answer 39

inducing an ac into the primary coil creates an alternating magnetic field
changing the magnetic field in the iron core
there is an induced voltage across the secondary coil

Question 40

define the generator effect

Answer 40

wires cutting magnetic field lines, including a voltage

Question 41

define a dc

Answer 41

a direct current
a current that only flows in one direction only

Question 42

define an ac

Answer 42

alternating current
a current which changes direction, between positive and negative values

Question 43

describe the differences between longitudinal and transverse waves

Answer 43

longitudinal: oscillations and energy transfers are parallel

transverse: oscillations and energy transfers are perpendicular