P15 Flashcards
What is an example of a non-contact force?
Attraction and repulsion between two magnetic poles
What are the two types of magnets?
Permenant or induced
What are permenant magnets?
Produce their own magnetic field
What are induced magnets?
Magnetic materials that turn into a magnet when put in a magnetic field
What are some examples of magnetic materials?
Iron,steel,nickel,cobalt
What is the force between induced and permenant magnets?
Attractive
What happens when induced take away magnetic field?
Lose magnetism
What happens when you put two magnets of pole near each other?
Exert a force on each other
What happens when two poles are the same?
They repel each other
What happens to two unlike poles?
They attract each other
Whats the magnetic field?
A region where other magnets or magnetic materials experience a force
What does the strength of the magnetic field depend on?
The distance from the magnet (strongest at the poles)
How is the direction of the magnetic field given?
Direction of the force that would act on another north pole.
What doees a magnetic field contain?
A bar magnet
How does a compass work?
Earth has a magnetic field and the compass points to the magnetic field
What happens when a current flows through the wire?
A magnetic field is created around the wire
What does the strength of the magnetic field depend on?
- Current of wire and distance
How can you increase the strength of a magnetic field?
Wrap the wire in Solenoid
How is the magnetic field in the solenoid?
Strong and uniform
How can solenoid increase magnetic field?
The field lines around each loop line up with each other. Closer the feild lines stronger they are
How can you increase the feild strength of a solenoid even more?
Put a block of iron in the centre of the coil
How are electromagnets used in cranes?
Used to attract and pick up thing made from magnetic materials. Switch is turned on to pick up things and switched of to drop things.
What is the motor effect?
When a current carrying wire is put between magnetic poles, the magnetic feild around the wire interacts with the magnetic field. This causes the magnet and conductor to exert force on each other
What are the factors that affect the size of the force on the conductor?
- Magnetic flux density
- the size of the current
- the length of the conductor
What is the equation when the current is 90° to the magnetic field?
F = BI1
What is B in BI1?
Flux density (tesla)
What is I in BI1?
Current (amps)
What is 1 in BI1?
Length (meter)
Explain the electric motor in breif terms?
A coill of wire carrying a current in a magnetic feild tends to rotate.
How does the force in a conductor cause the rotation of a coil in a electric motor?
The coil is on a spindle and the forces act one up one down
What do loudspeakers and headphones use?
Electromagnets
Why do loudspeakers and headphones use the motor effect?
To convert variation in current in electrical circuts to pressure variation of sound waves
How do moving coil loudspeakers work?
1) An alternating current is sent through coil of wire attatched to the base of the paper one.
2) the coil surrounds one pole so the current causes a force on the coil
3) when the current reverses the force acts in a opposite direction
4) variation in current make cone vibrate
What is the generator effect?
The induction of potential difference in a wire which is moving relative to a magnetic field.
What is an induced current?
Opposes the change that made it
What factors affect the size of induced potential difference?
1) increasing speed of movement
2) increasing strength of magnetic field
Give an example of the generator effect?
Moving a magnet in a coil wire or moving a conductor in a magnetic field
What do alternaters do?
Generate alternating current.
Explain how generator effect is used in alternator?
1) Alternator rotates the coil
2) As the coil spins a current is induced
3) acs have slip rings and brushes
What do dynamos produce?
Direct current
How do dynamos generate current?
1) Dynamos have split ring commutator instead of slip rings. This swaps the connection every half turn
How is ac shown on a graph?
Up and down
How is dc shown in a graph?
Above axis
How is increasing revolutions shown?
Up and down. Lots of peaks
How do microphones use the generator effect?
To convert pressure variations in sound waves in variations is current in electrical circuts
How does a moving coil microphone work?
1) Sound waves hit a flexible diaphragm that is attatched to the coil.
2) Causes the coil to move in the magnetic field which generates a current
What is a transformer?
Changes the size of the potential difference of an alternating current
What do transformers only work with?
Alternating currents
What does a basic transformer consist of?
A primary coil and a secondary wound on iron core
What is the potential differencecalculation?
Vp / Vs = Np / Ns
What are the ratios between primary and secondary?
Its the same between the number of turns on the primary and secondary
