P4 Magnetism Flashcards
Magnetism describes…
The ability of magnets to attract + repel other magnets without touching them
What are the two poles of a magnet?
North and south
A magnetic field is…
The area around a magnet where another magnet or magnetic material feels a force
What are four examples of magnetic materials
Iron
Nickel
Cobalt
Steel
The magnetic field is strongest where?
At the magnet’s poles
How can you make an iron nail magnetic?
By running a magnet repeatedly over the nail in the same direction
By making a nail magnetic it becomes an ____ magnet
Over time it will _____
Induced
Demagnetise
Magnetic field lines always point…
From north to south
The strength of a field is shown by?
How close together the field lines are
Bar magnets are _____ magnets and contain _____ magnetic domains
Permanent
Aligned
What is different about the Earth’s magnetic field?
The magnetic South Pole is in the northern hemisphere
What is the right hand grip rule
Thumb points along direction of current
Other fingers give direction of field
The magnetic field pattern around a _____ (coil) takes the same shape as that around a bar magnet
Strength of field increased by?
Solenoid
1. Adding more turns to coil
2. Increasing current
3. Adding iron core
What are 3 advantages of using electromagnets instead of permanent magnets?
- Can be switched on and off
- Can change its strength (increase/decrease current)
- Can swap their polarity
What is the motor effect
Putting a current-carrying wire in a magnetic field will produce a force
Why does the motor effect occur
Current in wire produces a magnetic field
This interacts with field of magnet
Produces a force
Only happens if wire cuts field lines
How do we predict direction of force for a motor?
Fleming’s left hand rule
What does each finger represent in Fleming’s left hand rule?
Thumb = motion
First finger = field
Second finger = current
What kind of current is shown by the second finger?
Conventional current (positive to negative)
How do we increase strength of force exerted in a motor?
F=BIL - increasing any of these will increase force
1. More current
2. Stronger magnet
3. More turns to coil
What is the role of a split ring commutator
To keep the coil rotating in the same direction
Explain how a loudspeaker works
- Current flowing through coil causes a force due to the motor effect
- Direction of force given by Fleming’s left hand rule
- As current alternates, diaphragm moves in and out
- Causes sound waves in air
What is the difference between motors and electromagnetic induction (generators)?
Motors have a current in a wire which produces a force
Generators have a moving wire which produces a current
When a coil of wire is rotated in a magnetic field…
An electric current will be generated
Direction of induced current in a generator is worked out using which hand rule?
Fleming’s right hand rule
What do the fingers represent in Fleming’s right hand rule?
Thumb = direction conducting wire moves (motion)
First finger = field
Second finger = current
What is a DC signal
One in which the electrons flow in one direction around the circuit
Explain how a DC generator works
Moving wire through field induces current
Split ring commutator means direct current is produced
Direction of current found using Fleming’s right hand rule
What is an AC signal
One in which the current switches directions, so the electrons move backwards and forwards about a point
Explain how an AC generator works
Moving wire through magnetic field induces current
Slip ring commutator produces alternating current
Direction of current found using Fleming’s right hand rule
Explain how a motor works
Coil of wire between poles of magnet
Current in the wire produces magnetic field which interacts with field of permanent magnet, creating a force
Direction of force found using Fleming’s left hand rule
Split ring commutator switches direction of current to allow motor to keep rotating
Permanent magnets always produce
Their own magnetic field
Temporary / induced magnets produce
A magnetic field only when they’re in the presence of another magnet
What are magnetically soft materials
Magnetic materials that gain and lose magnetism quickly
What are magnetically hard materials
Magnetic materials that gain and lose magnetism slowly
To experience the full force, a current carrying wire must be…
Perpendicular to magnetic field
An example of a magnetically soft material
Iron
An example of a magnetically hard material
Steel
The force between a permanent and induced magnet will…
Always be attractive
Magnetic field lines can show…
Strength of magnet at particular point
Whether 2 magnets would attract or repel
Direction a compass would point at that point
When an electrical current flows through a material…
A magnetic field is always produced
What is the function of a loudspeaker
To convert electrical signals into sound waves
Name three ways to increase size of potential difference generated in electromagnetic induction
Increase magnetic field strength
Move coil through field faster
Add more turns to coil
Difference between design of alternator and design of dynamo?
Alternator = slip rings
Dynamo = split ring
A wire moving up and down perpendicular to a magnetic field will…
Generate an alternating potential difference
When a wire experiences a ___ magnetic field, a potential difference will be ___
If the ends of wire are connected to make a ___ circuit, a ___ will flow
Changing
Induced
Closed
Current
A wire moving parallel to a magnetic field will
Not generate a potential difference
