Flashcards in physic paper 2 magnetism and electromagnetism Deck (45):
what do magnets produce?
a magnetic field
what is a magnetic field?
where magnetic materials experience a force
what do magnetic field lines show?
the size and direction of magnetic fields- north to south
what creates a uniform field?
placing the north and south poles of two permanent bar magnets near each other
how can you use iron filings to show magnetic field?
put magnet/s under a piece of paper and scatter the iron filings on top
how can you use compasses to find magnetic filed line?
use a compass and move it around the magnet tracing its position and direction
what does a current-carrying wire create?
a magnetic field
the larger the electric current...
...the stronger the magnetic field
what does the direction of the magnetic filed depend on?
the direction of the current
describe the motor effect
when a current-carrying wire is put between magnetic poles, the two magnetic fields affect one another. The result is a force on the wire causing it to move.
to experience a full force what degree does the wire need to be at to the magnetic field?
the force always acts in what direction?
relative to the magnetic field of teh magnets and the direction of the current in the wire
how is a horseshoe magnet used to show the direction of the force?
apply a current to a set of rails inside a horseshoe magnet. a bar is placed on the rails, which completes the circuit. this generates a force that rolls the bar along the rails
how does the magnitude (strength) of the force increase?
1-with the increasing strength of the magnetic field
2- the amount of current passing through the conductor
3-reversing the current or the magnetic field also reverses the direction of the force
what 4 factors speed up a D.C electric motor?
1) more current
2) more turns on the coil
3) stronger magnetic field
4) a soft iron core
how does a simple D.C electric motor work?
1- a current-carrying wire is placed in a magnetic field on a spindle
2- it rotates up and down due to the forces from the magnetic field
3- the split-ring commutator swaps the contacts every half turn to keep the motor rotating in the same direction
4- the direction of the motor can be reversed either by swapping the polarity of the d.c supply or swapping the magnetic poles over
how do loudspeakers work?
1) a.c. electrical signals from an amplifier are fed to a coil of wire in the speaker which is wrapped around the base of the cone
2)the coil is surrounded by a permanent magnet, so the a.c. signals cause a force on the coil and make it move back and forth
3) these movements cause the cone to vibrate causing sound as sound is a series of compressions through the air to the ear drum
what is electromagnetic induction?
the creation of a voltage and current in a wire which is experiencing a change in magnetic field
what is the dynamo effect?
using electromagnetic induction to transform KE into electrical energy
what are the 2 ways to get electromagnetic induction?
1) an electrical conductor- coil of wire- moves through a magnetic field
2) the magnetic field through an electrical conductor changes
test this by connecting an ammeter to a conductor and moving it through a magnetic field which will show the magnitude and direction of the induced current
to get a bigger voltage:
1) increase the strength of the magnet
2) increase the number of turns on the coil
3) increase the speed of movement
how does an A.C. generator work?
1) generators rotate a coil in a magnetic field
2) coil spins and a current is induced in the coil and this current changes every half turn
3) instead of a split-ring commutator it uses slip rings and brushes so the contacts don't swap every half turn
4) this means they produce a.c. voltage shown on CRO displays
5) faster revolutions produce more peaks and higher overall voltage
6) power stations use a.c generators to produce electricity
what do magnets affect?
magnetic materials and other magnets
what happens when a magnet is brought near a magnetic material?
that material acts as a magnet and this magnetism has been induced by the original magnet. the closer the magnet and the material get, the stronger the induced magnetism will be
what is there around a straight, current-carrying wire and what is it made up of? draw it
a magnetic field (right hand rule), which is made up of concentric circles
what's the magnetic field like around a flat circular coil? draw it
-the magnetic field in the centre of a flat circular coil of wire is similar to that of a bar magnet
- there are concentric ellipses of magnetic field lines around the coil
draw repelling and attracting magnetic field lines of two magnets placed near eachother
what's the magnetic field around solenoid like? draw it
1) the magnetic inside a current-carrying solenoid (a coil carrying wire) is strong and uniform
2) outside the coil, the field is like the one of a bar magnet
3) so the ends of a solenoid act like the north pole and south pole of a bar magnet. this type of magnet is called an ELECTROMAGNET
what's a soft magnetic material?
easy to magnetised but loses its induced magnetism easily
what's a hard magnetic material?
hard to magnetise but keeps its magnetism permanently
what's an example of a soft magnetic material?
what's an example of a hard magnetic material?
what is iron used for?
transformers because its soft so it can be magnetised and demagnetised 50 times a second- mains in UK runs at 50Hz
paper 2- why does a current-carrying wire feel a force when put in between magnetic poles?
because the charged particles moving through a magnetic will experience a fore, as long as they're not moving parallel to the field lines
what do transformers only work with?
what do transformers do?
change the size of the voltage of an alternating current?
what do transformers have?
two coils, primary and secondary, joined with an iron core
what happens when an alternating voltage is applied across the primary coil?
the magnetically soft core magnetises and demagnetises quickly. This induces an alternating voltage in the secondary coil
the ratio of the primary and secondary voltages is determined by what?
the number of turns on the primary and secondary coils
what do step-up transformers do?
step up the voltage- more turns on the secondary than the primary
what do step-down transformers do?
step the voltage down. they have more turns on the primary coil than the secondary
what's the transformer equation?
input primary voltage/ output secondary voltage= number of turns on primary/ number of turns on secondary
what's the equation for power in transformers?
input power= output power