electromagnetism

Question 1

State in what direction do field lines around a magnet go:

Answer 1

north to south

Question 2

List some magnetic materials:

Answer 2

-steel
-iron
-cobalt
-nickel

Question 3

What is the term when an object is made into a magnet

Answer 3

induced magnetism

Question 4

What is the difference between induced magnets and permanent magnets

Answer 4

permanent magnets produce their own magnetic field, where as induced magnets are placed into a magnetic field and can lose its force when removed.

Question 5

What are magnets?

Answer 5

magnets are objects that can make a non-contact force that repels or attracts.

Question 6

Describe how a current can cause a magnetic field:

Answer 6

A conductor with a current can develop a magnetic field only when the current is flowing. Making the current flow the other way will reverse the direction of the magnetic field.

Question 7

What symbols show that the field lines are coming out / in of a page in a diagram

Answer 7

out = circle with a dot in the middle
in = circle with a cross

Question 8

What is the motor effect?

Answer 8

the interaction between an external magnetic field and the magnetic field of an induce wire causing a physical force to be exerted on the wire.

Question 9

Write the equation relates magnetic flux density, force, current and length.

Answer 9

force (N) = magnetic flux density (T) x current (A) x length (m)

Question 10

Define magnetic flux density:

Answer 10

the strength of a magnetic field.

Question 11

What is Fleming’s left hand rule?

Answer 11

The rule which relates the direction of the current (middle), external field lines (pointer) and force (thumb) on a wire in a motor effect sample.

Question 12

What is Fleming’s right hand rule??

Question 13

What is the human hearing range?

Answer 13

20Hz- 20kHz

Question 14

Describe what sound waves are:

Answer 14

sound waves are longitudinal waves that have areas of compression and rarefaction

Question 15

Explain how a loudspeaker works:

Answer 15

1. an amplifier supplies an AC into a wire coil, making it generate its own magnetic field.
2. the coil is coiled around the permanent magnet, where the two magnetic fields interact and cause a motor effect.
3. the AC causes the coil to move out and in as the magnetic fields continuously repel and attract each other (the alternating current changes the direction).
4. the coil is attached to a flexible cone, and the motor effect causes a resultant force to move the the coil with the cone.
5. the repetitive movement cause sound waves to be generated

Question 16

What would you change in a loudspeaker to adjust the pitch and volume?

Answer 16

-to increase the pitch, you increase the AC
-to increase the volume, increase the voltage.

Question 17

What is the generator effect?

Answer 17

When a wire passes though a magnetic field, a potential difference is induced at the ends of the wire. Changing the direction of the wire passing will change the direction of the potential difference and when there is no movement there is no voltage generated. If you put a loop of a wire through a magnetic field the potential difference created will create a current in the wire

Question 18

How can you increase the impact of the motor effect?

Answer 18

-increase the current in the wire
-make the wire longer (coil it)
-increase the magnetic flux density of the external magnets
-make the two fields as perpendicular as possible

Question 19

How would you reverse the motor effect’s direction?

Answer 19

-reverse the direction the current in the wire
-flip the external magnetic field’s direction.

Question 20

How can you increase the impact of the generator effect?

Answer 20

-increase the magnetic flux density of external magnets.
-move the wire faster
-increase the mount of wire that passes through the magnetic field (coil it)

Question 21

How would you reverse the generator effect’s induced current’s direction?

Answer 21

-change the direction of movement
-switch the poles external magnet

Question 22

Explain how a current can be created when an ammeter circuit passes through a U-shaped magnet:

Answer 22

1. the north and South Pole of the magnet create its ow magnetic field, whose lines go from north to south
2. as the wire circuit passes through the magnetic field ad cuts it in one direction, a potential difference is created.
3. the potential difference pushes a current through the wire in one direction.
   4.this is detected and measured by the ammeter.
4. when the wire cuts the field lines in the opposite direction, the p.d reverses, generating an opposite current.

Question 23

in an electric motor, what does the split ring commutator do?

Answer 23

it reverses the current’s direction every half turn so that the motor effect doesn’t get counteracted when it fully turns, allowing the coil to move in one continuous motion rather than rocking back and forth to a rest vertically.

Question 24

In a generator, describe and explain the relation between the potential difference and position of a rotating coil suspended in a magnet’s magnetic field.

Answer 24

when the coil is parallel to the field lines, it generates the maximum potential difference because the wire is passing the field lines at its maximum velocity as much as possible.

when the coil is perpendicular to the field lines, the potential difference drops to 0 because its furthest away from the strongest point of the magnetic field and isn’t cutting them at all.

Question 25

Describe the wire in an alternator:

Answer 25

a wire with both ends connected to two different commutators which allow the induced current to flow out of the coil.

Question 26

Describe the wire in dynamo:

Answer 26

a wire with both ends connected to a split ring commutator which allows the potential difference to not shift directions, providing a direct current.

Question 27

Give ways on which we may increase the potential difference / frequency induced by an alternator.

Answer 27

P.D - - make the magnetic field stronger -increase the number of coils Frequency- -make relative motion quicker.

Question 28

Describe a graph showing the potential difference induced as a coil rotates in an alternator:

Answer 28

when perpendicular to the field lines, the p.d is at 0, when it starts to parallel, the p.d increases to its peak, as it completes half a rotation back to a vertical position, the p.d decreases to 0, when it continues to rotate to a parallel position the p.d increases to its peak, but is in the negatives as the p.d switches directions. this creates a graph where one full rotation looks like sideways s starting at the origin.

Question 29

Describe a graph showing the potential difference induced as a coil rotates in a dynamo:

Answer 29

when perpendicular to the field lines, the p.d is at 0, when it starts to parallel, the p.d increases to its peak, as it completes half a rotation back to a vertical position, the split ring maintains the direction of the current as it switches the wire ends even when the p.d changes direction. this means as it completes the second half of the turn, the potential difference peaks again in the positive side of the graph before going back to 0 as it becomes perpendicular. this creates an m shaped graph starting at the origin.

Question 30

What is a transformer and include examples:

Answer 30

an electrical device that changes the potential difference supplied by a supply to a different potential difference for an appliance. e.g a mobile charger, an adapter, a step up/down transformer.

Question 31

What are the main components of a basic transformer:

Answer 31

at least two coils (different amounts of coils) wound round a laminated iron core.

Question 32

What is the formula that relates the number of turns and the voltage in a transformer?

Answer 32

Number of coils (primary) / Number of coils (secondary) = Voltage of wire (primary) / Voltage of wire (secondary)

Question 33

How does a transformer work

Question 34

Explain how a relay uses electromagnets:

Answer 34

A relay switches an electric machine on and off using a small current to power something with a big current. A small current is supplied to a wire which flows through an iron core, an electromagnet is induced creating its own magnetic field. This attracts the armature and it closes the gap between two switch terminals, completing the circuit.

Question 35

Explain how a circuit breaker uses electromagnets:

Answer 35

when a too big of a current flows, it increases the magnetic flux density of the electromagnet. this force will then be strong enough to pull a piece of the circuit's conductor towards it, which breaks the circuit. in this way, if the current is too high or the electromagnet becomes too strong, it will be switched off.

Question 36

Describe how a scrap yard uses electromagnets:

Answer 36

to move magnetic materials around, a current is allowed to flow in a conductor, this creates its own temporary magnetic field (becoming an induced magnet) which attracts magnetic materials, picking them up. to release them, the current is switched off, and the induced magnet eventually loses its magnetic field, so drops the materials.

Question 37

Explain how an electric bell uses electromagnets:

Answer 37

a battery supplies a current through a wire to a conductor, inducing a magnet. the electromagnet's magnetic field then attracts an iron armature which rings the bell, whilst it moves it breaks the circuit so the current is stopped and the electromagnet loses its magnetic flux density and releases the armature closing the circuit. this means a current can flow again magnetising the iron core which repeats the cycle.