(Done) Magnetism (Paper 2) Flashcards
(43 cards)
1
Q
Define a magnetic field
A
- A region where other magnets or magnetic materials experience a force
2
Q
What type of force is a magnetic force
A
- Non-contact
3
Q
Where is the magnetic field the strongest
A
- At the poles of the magnets
4
Q
Where is the magnetic force the strongest
A
- At the poles of the magnet
5
Q
What direction is the force between a magnet and a magnetic material
A
- Attractive
6
Q
What are the two types of magnets
A
- Permanent
- Induced
7
Q
Define a permanent magnet
A
- A magnet that produces its own magnetic field
8
Q
Define an induced magnet
A
- A magnetic material that becomes a magnet when it is put into a magnetic field
9
Q
What type of force is always occurs between a permanent and induced magnet
A
- An attractive force
10
Q
What happens when an induced magnet is no longer within a magnetic field
A
- The induced magnet quickly loses its magnetism and stops producing a magnetic field
11
Q
What happens (relative to magnetism) when a current flows through a wire
A
- A magnetic field is created around the wire
12
Q
What makes up the magnetic field of a wire with current flowing through it
A
- Concentric circles perpendicular to the wire with the wire as the centre
13
Q
Define concentric circles
A
- Circles that share the same centre
14
Q
What happens to the magnetic field of a wire when you change the direction of current
A
- You change the direction of the magnetic field
15
Q
What factors affect the strength of the magnetic field of an electromagnet
A
- The size of the current flowing through the wire
- The distance from the centre of the magnetic field
16
Q
Define a solenoid
A
- A coil of wire that can create a magnetic field when an electric current passes through it
17
Q
What are the properties of the magnetic field within a solenoid
A
- Strong
- Uniform
18
Q
How can you increase the magnetic field strength of a solenoid
A
- Placing a block of iron in the centre of the solenoid, which becomes an induced magnet
19
Q
What name is given to a solenoid with an iron core
A
- Electromagnet
20
Q
Uses of electromagnets
A
- In circuits as switches
- To pick things up
- Headphones and speakers
21
Q
Define the motor effect
A
- When a current carrying wire is placed between magnetic poles, the conductor and the magnet exert a force on each other
22
Q
What does the motor effect cause
A
- Movement of the wire
23
Q
What conditions are required for a wire to experience the full force of the motor effect
A
- The wire must be 90 degrees to the magnetic field
24
Q
What happens to the force of the motor when the wire runs parallel to the magnetic field
A
- The force is nullified
25
What direction is the force always exerted in the motor effect
- At a right angle to the magnetic field of the magnets and the direction of current in the wire
26
What factor affect the size of the force in the motor effect
- The strength of the magnetic field
- The amount of current passing through the conductor
27
What factors affect the force acting on a conductor in a magnetic field
- Magnetic flux density
- Size of the current through the conductor
- The length of the conductor in the field
28
What conditions are required to use the equation for the force in the motor effect
- When the flow of current is 90 degrees to the magnetic field it is in
29
What do the fingers correspond to in the Fleming left hand rule
- Thumb corresponds to the direction of the force
- First finger corresponds to the direction of the magnetic field
- Second finger corresponds to the direction of current
30
Function of a split-ring commutator
- Swaps the contacts every half turn to keep the motor rotating in the same direction
31
How can the direction of a motor be reversed
- Swapping the polarity of the DC supply (reversing the current)
- Swapping the magnetic poles (reversing the field
32
Define the generator effect
- The induction of a potential difference (and current if there is a complete circuit) which is moving relative to a magnetic field, or experiencing a change in magnetic field
33
What does the generator effect cause
- A potential difference in a conductor, as well as a current if the conductor is part of a complete circuit
34
How can the generator effect be induced
- Moving a magnet in a coil of wire
- Moving a charged conductor in a magnetic field ('cutting' magnetic field lines
35
How do generators produce ac or dc current
- As you turn the magnet, the magnetic field though the coil changes
- This change in magnetic field induces a potential difference, which causes charge if connected to a circuit
- When the magnet has reached a half turn, the polarity of the magnet has reversed so the magnetic field has reversed, causing the potential difference and therefore current to reverse
36
How does induced current always try and act
- Against the change that made it
37
How can induced potential difference be changed
- Increasing the speed of the movement - cutting more magnetic field lines in a given time
- Increasing the size of the magnetic field
38
How do alternators produce an alternating current
- Alternators rotate a coil within a magnetic field
- Alternators have slip rings instead of split ring commutators so the direction of the force does not change
- The constant rotation causes the polarity of the current to be constantly changing, causing an alternating current
39
Differences between a dynamo and an alternator
- Dynamos have split-ring commutators so so when direction of current alternates in the coil, the direction of current in the circuit remains the same
40
How are oscilloscopes used
- To show how the potential difference generated in a coil changes overtime
41
How do microphones work
- Sound waves cause the diaphragm to vibrate
- The diaphragm causes the coil to vibrate
- Inducing an alternating current in the circuit
42
How do transformers work
- They have two coils of insulated wire, primary and secondary, wrapped around an iron core
- When an alternating potential difference is applied through the primary coil, the magnetic field of the core changes quickly
- This changing magnetic field induces an alternating potential difference in the secondary coil
43
What is the relation between potential difference in a transformer and amount of coils
- The ratio of turns in the wire between the primary and secondary coil is the same as the ration of the potential difference in the primary and secondary coils
