Revision topic 15 Flashcards
what is the magnetic compass
it is a compass with a tiny magnetic nedel pivoted at its center, and since the earth, the magnetic field is concentrated at the magnetic north and south pole allows one end of the compass is pointing north and the other pointed south
what can be magnetized
iron and steel, and all ferrous material and some nonferrous material like cobalt and nickel.
what is a magnetic field
the space around the magnet
what happens to the magnetic field lines
lines in a bar magnet would curve from the north pole to the south pole
what happens in induced magnetism
unmagnetized magnet material can be magnetized by placing it in a magnetic field inducing it
explain how iron can be induced
when you place an iron in a magnetic field the rod poles closest with the magnet poles would become an opposite polarity making an attraction between the iron rod and the magnet, and if you remove iron from the magnetic field it would lose all its magnetism
in a uniform field, the lines of the magnetic field are
parallel to each other
when an electrical current passes along a wire what will happen
a magnetic field around the wire is set up, which can be seen by iron filling, the magnetic field would be strongest near the wire, and if we reverse the current the direction of the magnetic field would be reversed
how can you set up and prove that a magnetic field is stronger near the wire and that when the current is reversed the direction is reversed
take a battery, a wire, and a wooden stand (eliminate magnetism caused by a near object like iron), and a current carrying wire, a plotting compass, and a paper, so take a paper and hang it on the wooden stand perpendicularly then take a current carry wire and place it through the paper and connect it with a wire going through it that is connected to a battery
to prove that reversing the current reverse the direction:
you would take a compass and place it on the paper and turn on the current and see how the arrow moves then reverse the current and you would see the arrow move in the opposite way
to prove that the magnetic field gets stronger when we are closer to it:
take a compass and start moving away from the magnetic field after you move away from enough the compasses arrow would point at the north (earth natural magnet)
the magnetic field lines around the wire
are in circles centered on the wire in a plane perpendicular to the wire
what is a solenoid
it is a long coil of insulated wire
what happens when an electrical current passes through a solenoid
a magnetic field would appear around it, that would be stronger and more uniformed inside the solenoid, and its direction would be reversed if the current is reversed, and it increases in strength if the current increases
what are electromagnet made up from
they are made up of insulated wires around an iron bar, so when the current passes through the iron would be magnetized
electromagnets are used in
- the scrapyard crane
- an electrical bell
- the relay
what is the motor effect
it is when an electrical motor works because the force can act on a wire in a magnetic field while a current is passing through the wire
the size of the force in a motor effect can be increased by
- increasing the current
2. and using a stronger magnet
in the motor effect, what does the size of the force depend on
the angle between the wires and the magnetic field, as the force, is at its strongest when the wire is perpendicular to a magnetic field, and it’s at its zero if it was parallel to the magnetic field
in motor affect the direction of the force is always
at right angles with the wires and the field lines, and the direction would be reversed if the current was reversed
how can you use fleming righthand to determine where everything is
the first finger = the magnetic field
the second finger = the moment of the current
the third finger = the movement of the force
what does a simple motor consist of and how does it work
it consists of a rectangular coil made of insulated wire that is connected to the battery via graphite brushes that press against a metal split-ring commutator
so when a current passes through the coil would spin because a force would act on each side of the coil due to the motor and the force of one side acts in the opposite direction of the other side, the split ring commutator would reverse the current passing through the wire at every half-turn of the coil, because of this the current of the half beside each pole in that magnet would remain in the same direction making the coil remain in the same direction
explain how a loudspeaker would constantly make the diaphragm vibrate
when the current moves through the coil it would be forced to move because of the motor effect, so each time the current changes its directions the force reverses its direction so the coil would repeatedly go back and forth and this moment would cause the diaphragm to vibrate so that sound waves are created
what does generate contain
a coil of wires that spin in a magnetic field
what is electromagnetism induction
it is the process where the potential difference is induced across the end of the wire when it cuts across a magnetic field
how can we test for the generator effect
we would set up an insulated wire to an ammeter then take the wire to move it between the poles in the u-shaped magnet and observe the ammeter, you would discover that the pointer would deflect as the current is generated when the wire cuts across the magnetic field. this is because the potential is induced in the wire when it cuts the magnetic field, this effect is called the generator effect
in the test for the generator effect, what should we find
- that no current is generated when the wire is stationary
- a current can be generated if the magnet instead of the wire is moved
- a larger current is generated when the wires move quickly
- the current is reversed when the direction of motion is reversed
explain the generator test
you would have a coil of insulated wire connected to an ammeter then you would have a magnet bar and you would put one side of the bar it the coil and the ammeter would deflect and that is because the movement of the bar causes the potential difference to be induced causing a current I would get induced no mater the pole because it can get induced in different directions.
what is a simple alternator made up of and what they are
they are alternating currents it is made up of a rectangle coil that is forced to spin in a uniform magnetic field, the coil is connected to the center-reading meter via the metal brushes that press upon the 2 split ring commutator, the metal brushes, and the 2 split ring commutator provides a continuous connection
explain how an alternator works
so the coil would move steadily in one direction causing the pointer in the meter to deflect away then deflect the opposite way then back again and this would continually happen if the coil stays moving in one direction so form this we can say that the current and the potential difference in the wire are alternating.
how does the induced potential difference vary in alternators
- the size of the induced potential difference is greatest when the plan of the coil is parallel to the magnetic field
- the size of the potential difference would be zero if the plan of the coil is peduncular to the magnetic field
the faster the coil rotates in alternators?
- the greater the frequency of the alternating current
2. the larger the peak value of the alternating current which can also be increased by using a magnetic field
what is a dynamo and what is it made up form
it is made up of a rectangular coil, that is connected to a centre-reader meter via metal brushes that press up upon the split ring commutator
how does dynamo current work
as the coil spin, the split ring commutator would reconnect into the opposite direction every half turn, this would happen each time the coil is particular to the magnetic field because of this the induced potential difference doesn’t go in reverse directions, the induced potential difference varied from zero to maximum value twice each cycle, never changing polarity
what happens in a microphone
the sound waves make the coil vibrate in the magnetic field causing an altering voltage to be generated
what is the national grid
electricity delivered via a network of cables
what is a transformer used for
it is used to change the potential difference between the power station and the cables and between the cables and your home
how do transformers work
a transformer would two coils of insulated wires connected on the same iron core that can be easily magnetized and demagnetized, the primary coil is connected to an altering current, so when the altering current passes through the primary coil, an altering potential difference is induced in the secondary coil, this would happen because:
altering current passing through a coil would an altering magnetic field, the line of the magnetic field would pass through the coil as the magnetic field is changing this would create an altering potential difference between the terminals in the secondary coils, if a light bulb would be connected to the on the secondary coil the induced potential difference would light up the bulb, as the electrical signal is transferred from the primary coil to the secondary coil
what is a step-up transformer
a transformer where the potential difference across the secondary coil is higher than the primary coil because the secondary coil has more turns
what is a step-down transformer
a transformer where the potential difference across the primary coil is higher than the secondary coil because the primary coil has more turns
what is the difference between a normal transformer and a switch-mode transfer
- switch mode transfer operates at a higher frequency, it is much smaller and lighters, and it uses very little power when no electrical device is connected to
why are transformers used
because the higher the grid potential difference the more efficient it is to transfer electrical power through the grid this is why transformers are used to step up the potential differences from the power station to the grid and to step up the potential difference from the grid to the mains voltage
what is the transformer equation
V(p)/ V(s) = N(p)/N(s)
what is the transformers efficiency equation
the transformers are always almost a 100% a efficient and the equation would go as
V(p) x I(p) = V(s) x I(s)
