P4 - magnetism and magnetic fields Flashcards
what is an alternator?
also called AC generator
what is current?
rate of flow of charge
`what is a diaphragm?
the part of a loudspeaker that moves to produce a pressure wave in the air i.e. sound
what is a dynamo?
also called DC generator
what is electromagnetic induction?
the process of producing an induced potential difference in a conductor due to the conductor cutting magnetic field lines
what is a generator?
a device that converts KE into electrical energy; consists of a rotating wire in a magnetic field
what does induced mean?
to bring about; make happen
what is magnetic flux density?
same as magnetic field strength
what is a motor?
a component that produces rotation from the combination of the fields due to magnets and current carrying wires
what is a solenoid?
a coil of wire used in an electromagnet
what is a split ring commutator?
keeps the coil rotating in the same direction by reversing the direction of current every half turn
what is a transformer?
a component that uses two coils and an iron core to change the potential difference in a circuit
what is a Tesla?
the unit of magnetic flux density
what is a magnetic field?
a region where a magnetic material will experience a force
magnetic field lines always point …
from north to south
the strength of the field is shown by …
how close the field lines are to eachother
the magnetic field is always strongest …
at the poles
what are the only 3 magnetic elements?
- iron
- nickel
- cobalt
what are bar magnets?
- permanent magnets
- contain aligned magnetic domains
- retain their magnetism and so are called magnetically hard materials
what does an iron nail have?
randomly aligned domains
what will happen to an iron nail when placed in a magnetic field?
- the domains will line up, producing an induced magnet
- by banging the magnet the domains then randomly align again because the nail is made of a ‘soft’ magnetic material
how do we know the Earth has a magnetic field?
where does it come from?
- the Earth’s magnetic field is caused by iron ions moving (convection currents) inside the Earth’s core
- we know the shape of the Earth’s magnetic field because scientists take compasses around the world and are able to map the magnetic filed lines since the compasses line up with them
- the North Pole of a magnet is attracted to the geographic North Pole of the Earth because there is a magnetic South Pole there
when an electric current flows in a wire, what shape is the magnetic field it produces?
circular
what does the direction of the field depend on?
the direction of the current
as the distance away from the wire increases, what happens to the field strength?
it decreases
how do we show the magnetic field strength decreasing as distance increases?
the field lines getting further apart
what does the magnetic field pattern around a solenoid take the same shape as?
as that around a bar magnet
what can the strength of the magnetic field be increased by?
- more turns on the coil/loops
- more current/increase the current
- add an iron core
investigation:
how does increasing the current in a solenoid affect the strength of the electromagnet?
- what are the variables in this investigation?
dependent variable = number of paperclips picked up
independent variable = current
control variables = size of paperclips, nail, no. of turns in solenoid
method for investigation for how does increasing the current in a solenoid affect the strength of the electromagnet?
- set up circuit
- use variable resistor to adjust/vary he current to chosen values e.g. 0, 0.25, 0.5, 0.75 etc
- at each current, place the nail into a pile of paperclips and record how many are picked up
- repeat the experiment so you have three values of paperclips for each current value
- calculate the mean average paperclips and plot data onto a graph
what is formed when a current flows through a solenoid?
a magnetic field