Magnetism and Electromagnetism - Physics Paper 2 Flashcards
What does a magnet have around it?
A magnetic field
What is a magnetic field?
A region where magnets experience a force acting on them
What type of force is a magnetic force?
A non-contact force
What can a magnetic field be represented by?
A field diagram
How many poles do magnets have?
2
What are the 2 poles called?
North and South
What do the arrows on magnetic field lines point to?
from north to south
What do the direction of magnetic field lines show?
The direction of the force the north pole would feel if it was placed in that location
The stronger the magnetic field at any point…
the closer together the field lines are
What do like poles do?
Repel
What do unlike poles do?
Attract
What’s inside a compass?
A tiny bar magnet
What are the 2 types of magnets?
Permanent and induced
What do permanent magnets do?
They produce their own magnetic fields
What are induced magnets?
Magnetic materials that turn into magnets when they’re in a magnetic field
What happens when you take a magnetic field away from an induced magnet?
It loses its magnetism
What are examples of permanent magnets?
Bar magnets and horseshoe magnets
What are some examples of magnetic materials?
Iron, steel, nickel, cobalt
What happens when a current flows through a wire?
A magnetic field is created around the wire.
What is the right-hand thumb rule?
You use your right hand and point your thumb in the direction of the current, and curl your fingers. The direction of your fingers is the direction of the field
The larger the current through the wire, or the closer to the wire you are…
the stronger the field is
How can you increase the strength of the magnetic field that a wire produces?
by wrapping the wire into a coil called a solenoid
How can you increase the magnetic field around a solenoid even further?
By putting a block of iron in the centre of the coil. The iron core becomes an induced magnet whenever current is flowing . The magnetic field of the core and the coil combine, making a stronger magnet overall.
What is a solenoid with an iron core called?
An electromagnet
Can electromagnets be switched on and off?
Yes
What is the motor effect?
When a current-carrying wire in a magnetic field experiences a force
How do you calculate the force on a wire carrying a current at right angles to a magnetic field?
force = magnetic flux density × current × length
What are the units of magnetic flux density?
Tesla (T)
What is magnetic flux density?
How many field (flux) lines there are in a region. This shows the strength of the magnetic field.
If a current is flowing at 90 degrees to a magnetic field, how can you tell which way the force is acting on the conductor due to the motor effect ?
Using Fleming’s left-hand rule
How do you use Fleming’s left hand rule?
Hold your thumb, forefinger and second finger at right angles to each other:
- the forefinger is lined up with magnetic field lines pointing from north to south
- the second finger is lined up with the current pointing from positive to negative
- the thumb shows the direction of the motor effect force on the conductor carrying the current
How can the speed of an electric motor be increased?
- By increasing the current
- By increasing the strength of the magnetic field
The direction that a motor turns in can be found using Fleming’s left hand rule and can be reversed either by….
- swapping the polarity of the dc supply
- swapping the magnetic poles over
What allows loudspeakers to work?
The motor effect
What is the generator effect?
The generator effect is the induction of a potential difference across a conductor which is experiencing a change in an external magnetic field
Which ways can the potential difference across the ends of a conductor be induced?
- By moving the electrical conductor in a magnetic field
- By moving or changing a magnetic field relative to the electrical conductor
How can induced potential difference be increased?
- Increasing the speed of the movement
- Increasing the strength of the magnetic field
What do alternators do?
They generate an alternating current
What do dynamos do?
They generate direct current
What can you use an oscilloscope to see?
how potential difference generated in the coil changes over time
What are microphones basically?
Loudspeakers in reverse that generate current from sound waves
What are transformers?
Devices that can change the potential difference of an electrical supply using the generator effect.
What is the structure of transformers?
They consist of 2 coils, the primary and secondary, wrapped around an iron core. Iron is used as a core because it magnetises and demagnetises quickly.
Why is iron used as the core of transformers?
Iron is used as a core because it magnetises and demagnetises quickly.
What are the 2 types of transformers?
The step down transformer and the step up transformer
What happens in step-up transformers?
The number of turns on the secondary coil and the size of the pd across it are greater than across the primary coil.
What happens in step-down transformers?
The number of turns on the secondary coil and the size of the pd across it are smaller than across the primary coil
What is the transformer equation?
potential difference across primary coil / potential difference across secondary coil = number of turns on primary coil/number of turns n secondary coil
potential difference across secondary coil X current in secondary coil =
= potential difference across primary coil X current in primary coil
