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P4- Magnets Flashcards

1
Q

Define a magnet

A

A material or object which produces a magnetic field

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2
Q

What must all magnets have

A

A north and a south pole and are surrounded by a magnetic field

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3
Q

How do you represent magnetic feilds

A

By using field lines

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4
Q

Which directions must field lines point

A

From the north pole to the south pole

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5
Q

How can you show where a magnetic field is strongest

A

By the denisty of the lines

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6
Q

How do you show a strong magnetic field in a diagram

A

Using densly packed field lines

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7
Q

What can you use to determin the north and south pole of a magnet

A

Using a compass

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8
Q

What are the difference between permanent
and induced magnets

A

Periminate magnets have there own magnetic fields but induced magnets become a magnet when they are placed in a magnetic feild

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9
Q

What are the 3 naturally magnetic elements

A

-iron (Fe)
-cobalt (Co)
-nickel (Ni)

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10
Q

What is the motor effect

A

A wire carrying a current creates a magnetic field. This can interact with another magnetic field, causing a force that pushes the wire at right angles

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11
Q

What hand do you use to work out the direction of current

A

Left hand

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12
Q

When using flemings left hand rule what does your thumb represent

A

The direction of the force

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13
Q

When using flemings left hand rule what does your fore finger represent

A

The direction of the magnetic field

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14
Q

When using flemings left hand rule what does your middle finger represent

A

The direction of the current

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15
Q

How do you arrange you fingers in flemings left hand rule

A

All at 90 degrees to one another

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16
Q

What does a split ring commutator do

A

Switches the postive and negitve connections every half turn

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17
Q

Why is a split ring commutator used

A

It makes it so that the forces are always acting in the same direction which makes the coil turn the full 360 degrees

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18
Q

How can you increase the speed of the rotation in an electric motor

A
  • Increase the currents
  • Add more coil
  • Use stronger magnets
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19
Q

What can the generator effect also be refered to as

A

Electromagnetic induction

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20
Q

What happens when you move a wire coil through a magnetic feild

A

It induces a potenial difference in a wire

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21
Q

What happens to a coil when you stop moving it through a magneitc field

A

The potential differnce dissapears

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22
Q

What causes the potenial difference in a wire in a magnetic feild

A

The change in the magnetic field is what induces a potential difference

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23
Q

What happens when you change the direction of the wires movements in a magnetic feild

A

The direction of the potential difference changes each time in changes direction

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24
Q

What happens when you move the coil wire along the mangetic field ( back and forth)

A

No potential difference or current will be induced because there is no change in magnetic field

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25
What happens when you close coil when it is moving through a magnetic field
A poteinial difference and a current is induced
26
How do you increase the size of the potential difference in a coil moving through a magnetic field
- Stronger magnets - Move the magnets faster - Shape the wire into a proper coil
27
How does using stronger magnets increase the potenial difference
Stronger magnets= Stronger magnetic field= Bigger potential difference
28
How does moving the magnetic faster increase the potenial difference
Faster movements = Faster magnetic field will change = Bigger potential difference
29
How does shaping the wire into a coil increase the potenial difference
More turns in the wire = Bigger poteinal difference
30
Define a solenoid
A solenoid consists of a wire coiled up into a spiral shape. When an electric current flows, the shape of the magnetic field is very similar to the field of a bar magnet
31
What is the magnetic field strength of a solenoid
Strong and uniform.
32
What are generators
Devices generate electricity from rotational motion
33
What are 'Alternators' and 'dynamos'
Different types of generators
34
How do Dynamos create electricty
They use a split ring comunitator in an electric motor
35
How do Alternators create electrcity
They use slip rings and brushed in an electric motor
36
What type of current do Dynamos produce
Direct current (d.c)
37
What type of current do Alternators produce
Alternating current (a.c)
38
How do slip rings and brushes work
Slip rings maintain constant contact with the same sides of the coil.
39
What happens to the current in an Alternator as the coil rotates faster (terms of a graph)
The peaks and occalations of the current on a graph get larger
40
Define an induced magnet
Any object that can be influenced by magnetic fields, and has the potenial to become a magnet
41
What are the commen magetic materials
- Nickle -Cobalt -Iron -Alloys of the 3 (steel....)
42
Are induced magets perminant
No they are only magnets temporarly when in a magnetic field
43
How do create an induced magnet
Place a piece of magnetic material(which wasnt actually a magnet) into the feild of a magnet. This induces its own magnetic field.
44
Which type of force will there always be between induced and perminate magnet
The force will allways be attractive- North to south
45
What materials are magnetically soft
- Nickle - Iron
46
Define Magnetically Soft
A material that loses its magnetism quickly when taken out of a magnetic field
47
Define Magnetically Hard
A material that loses its magetism slowly after being removed from a magnetic field
48
What materials are Magnetically hard
- Steel
49
What happens when you pass a current through a wire
A magnetic field is induced
50
What does the right hand rule show you
The direction of a mangetic field in a wire
51
How do you use the right hand rule
Curl your hand into a fist and point your thumb in the direction of the current . The direction your fingers are curled in is the direciton of the current.
52
What shape is the magentic field lines on a wire
Concentric circles
53
What shape are the magentic field lines in a circlular coil
Elipses and a line straight through the middle
54
What is the magnetic field of a soleniod simialar to
It is similar to the magnetic field of a bar magent
55
Which way do the arrows point in a magnetic field diagram of a solenoid
From North to South
56
What is a solenoid also known as
An ElectroMagnet
57
What happens when you stop the current through an Electrogmagnet
The magentic field stops
58
How do you reverse the direction of the magentic field in an Electromagnet
Reverse the direction of the current
59
How do you increase the strength of an electromagnet
- Increase the current in the solenoid - Increase the no. of turns (keep lenght the same) - Decrease the lenght of the coil (keep turns no. the same) - Add a soft iron core
60
How does the denisty of the turns in a solenoid effect the mangnets strength
Densly packed coils have a strong magentic field and less densly packed coils have a weaker magnetic field strength
61
How does adding a soft iron core effect the solenoids strength as a magnet
As iron is a soft magnetic material it will become an induced magnet when the solenoid is switched on which increases the magnetic field. It will also lose its magnetic field when the current is switched off
62
Define the motor effect
A current carrying wire in the presence of a magnetic field will experience a force
63
What is the eqaution for force experienced by a wire (during the motor effect
Force = current x magnetic field strenght x length of wire
64
What is another phrase for magnetic field strength
Magnetic flux density
65
What is the magnetic field strength mesured in
Teslas (T)
66
What is an oscilloscope
A volt meter that shows how voltage varries over time
67
What does the oscilloscope graph of an alternator look like
As the current switches direction the oscillations are on both the positve and negitive sides of the graph
68
What happens to an oscilloscope graph of an generator when the coil rotates faster
The oscillations get larger and more frequent
69
What does the oscilloscope graph of an dynamo look like
As the current is always flowing in the same direction the oscillations always stay on either the positvie or negitve sides of the graph
70
What the role of a transformer
To increase of decrease the voltage
71
What are transformers used for in the real world
To increase the volatage of electricty made in power stations so they can be transported around the country and to decreace the voltage when it reaches homes
72
What is a step up transformer
A transformer that increases the voltage decreases the current
73
What is a step down transformer
A transformer that decreases the voltage increases the current
74
What are the parts of a transformer
A primary coil A secondry coil An iron core
75
What is the coil ratio in a step up transformer
The primary coil has less turns that the secondry coil
76
What is the coil ratio in a step down transformer
The primary coil has more turns than the secondry coil
77
What type of current must be used in a transformer
An alternating current
78
How do transformers work
1. When supplied with an alternating current, the primary coil will generate a magnetic field 2. This then induces an alternating magnetic field in the iron core 3. This induces an alternating voltage in the secondry coil which (if the circit is complete) leads to an alternating current in the secondry coil
79
The ratio of turns in the primary and secondry coil affects...
The current and voltage in the secondry coil
80
What are the wires in transformers covered in
They are insulated in plastic

Physics (11 decks)

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