P4.2 Flashcards
What happens when a current carrying wire or a conductor with current goes into the field of magnet?
Why does this happen?
When is the force exerted at its maximum point?
EQUATION FOR SIZE OF FOCRE
Doesn’t happen when conductor is parallel actually
- a force is exerted on the wire
2) when the magnetic field of the wire interacts with the magnet, the fields add up if they are in the same direction. This Produces a ‘catapult field’ which in turn makes an effect. Here there are more stretched lines above their and less below the wire, causing it Catt in that direction, so that the magnetic lines straighten again (moves to straighten the lines)
3) when the wire is 90° to the magnetic field. This ensures all the magnetic field lines are cut by the magnetic field, exerting a greater force, this goes down and down until the wire is parallel to magnetic field, in which the force is 0.
F=BIL
Motor effect and 6 marker explanation?
How do you increase size of force in motor?
(COILS!!)
Motor effect: when electricity is used to make a force
1) when a current carrying conductor cuts a magnetic field perpendicularly, a force will be exterted on the wire
2) since the coil is on a spindele, and according to left hand rules the force is acting on both sides, it will rotate.
3) when it reaches 90°, it would continuously stay 90 because of the Fleming rule. To solve this, when the coil reaches 90°, the split ring commutator. At 90, the commutator briefly loses connection with the circuit, but it still turns due to momentum and gravity, and then the circuit comes back but now the direction of current going into the coil SWAPS.
4) this ensures that the forces acting on the coils stay the same and allows it to rotate in
1) increase the number of coils
2) increase magnetic field strength
3) increase current
4) increase length of coil (due to f=bil(
Summary
1) currrtn carrying conductor cuts magentic fiel lines perpendicularly force induce
- current going different directions both side so diffferent fixes, spindle, rotate
3) 90 would stay like it is due to Fleming, but that’s why split ting used, here sconenctiin s briefly lost still goes momentum, then connection regained, but direction of current going in coil is now swapped.
4) This ensures that original direction of force is maintained and full slim
How do loudspeakers work ( with a:c current)?
How to change frequency or volume of sound
1) when a current is flowing through the coils, a force is exerted due to the motor effect. This also exerts a force the cone
2) as ‘tis ac current, the current changes direction, and the force exerted on the coil is reversed and on the cone
Remember that this force is because of magnetic field generated by current which interacts with permanent magnet causing it to attract / repel
3) as current alternates, the coil moves back and forth
- this makes the cone vorberatende, creating PRESSURE VARIATIONS IN THE AIR, which is sound
The frequency of the current = frequency of sound , and if you increase size of current, ap,Touré of vibrations and volume increase too
Electromagnetic induction and generator effect
Properties of the current induced : how to reverse and increase pd induced
What two instances cause electromagnetic induction to happen ?
Generator effect uses relative motion to produce a current
When a conductor cuts perpendicularly a magnetic field, then it will induce a potential difference . (Induced potential difference Ehen a conductor experiences a changing magnetic field.)
2) when it is connected in a circuit, current will be in the circuit, and this is how we get electricity.
1) the current produced will reverse direction if the direction of rotation is reversed
2) the current increases if there are more turns in the coil, the magnetic flux increase or the speed of rotation increase
This is because more magnetic field lines are cut per second, giving a higher current
1) when a conductor and a magnetic field move relatively (so cut field lines)
2) or when a conductor experiences a change of magnetic flux
A.c alternator generator work
Also how does do against time graph look like
Ac produces ac current, which changes direction
1) when a coil is moved , it cuts the magnetic field lines of the field, this causes a current to be produced in the circuit.
2) However with slip rings , one end of the coil is PERMANENTLY ATTACHED to the slip ring.
3) when a given side of the coil is moving in one direction, current will flow through it in one direction , and exit through the slip ring commutator that is permanently attached to the end of a coil
4) when the same side moves in the other direction, then current will flow in the opposite direction (due to Fleming). Again it will exit in the other commits to as its permanently attached.
3) this means a in a rotation, the same end of the coil will have current going in it in both directions, as the direction of the current changes in the circuit,. (Current edits in both slip ring ends…) = a.c current
The graph of pd against time is like sin graph. Because current exits in both directions, it goes to the negative end too.
1) When the coil is vertical to the magnet, the coil stops cutting magnetic flux so current no longer induced so 0
2) when it is horizontal it cuts more and horizontal is the maximum it can cut so maximum induced
3) turns again to vertical so 0
4) turns again to horizontal so maximum but in opposite direction so negative
5) turns again to complete rotation and is at 0 as it’s vertical. In every rotation, current exits in both directions…
How I’s energy conserved in electrical induction
Or what about a current carrying wire
the current produced will have its own magnetic field too, which will move to opposes the original magnetic field. The induced magnetic field will repel the magnetic field that created it.
this idea is now energy is conserved and we don’t get infinite current.
Work must be done against the MAGNETIC FIELD, as it repels it, to produce the current, AND SO ENERGY IS PUT IN , KINETIC TO ELECTRICAL.
This energy is transferred to electrons in circuit making them move= current
Therefore nervy isn’t created, just transferred
2) similarly when current induced by motor effect force will be applied upwards, so opposing your force, work has to be done against this if you want to produce electricity
How dc generator work
1) when a conductor cuts he magnetic flux , a current is induced.
2) however the split ring commutator ensures that current can always exit in the same terminal, meaning the current had the same direction all the time. This is because the contact brushes points swap every half turn rather then being permanently stuck to one end of the coil
The graph would be just jumps . When horizontal and parallel, the current no longer induced, but the direction always same, so never goes negative…..
Ofc if the direction of rotation is changed the direction of current changes too….
How microphones work with generator effect
What does the frequency of sound =
1) similar to loudspeaker, but instead of a cone, a diaphragm is used.
2) as changes in pressure happen, the diaphragm moves back and forth when hit by these.
- compressions cause it to move in and rarefactions cause it to move out .
3) as the diaphragm moves, the coil of wire moves, and as it is a conductor cutting magnetic field lines,a pd is induced too and depending on the pressure variations will make different current variations. As the force changes direction, the direction of current changes too, meaning ac current is produced .
4) as the coil vibrates , an alternating current is produced not dc. Just opposite to loudspeaker with a diaphragm… YOU CAN ALSO JUST SAY A CHANGING PD IS INDUCED HERE
The frequency of sound = frequency of this changing pd
What do transformers do and how do they work
Where are more coils in primary vs secondary ones…
- Transformers step up or step down the pd of an alternating current.
If you know that one magenetic field turning on can generate a current on another magnetic field by transferring its magnet field, you know how transformers work…
1) a transformer is made up of a primary coil, a secondary coil and an iron core
2) A.C current given to primary coil, and so an alternating (keep changing) magnetic field is produced around the coil, and magnetises the iron core similarly, so the iron core carries the alternating magnetic field over.
3) this changing magnetic field causes an alternating of to be induced in the secondary coil (Fleming= magnetic field, changes and cuts through the conductor, so current induced)
1) Step up have more in secondary then primary, step down have more in primary then secondary .
Since power =VI, then the secondary will either have more current less voltage, or less voltage more current
Equation for ratio for pd and number of coils
V1/ v2 = n1/n2
Pd on first over pd of second= number of coils in first/ number of coils on second.
1st/ 2nd always, voltage and number for both…
Magnet falling down
Magnet falling down means a conductor is experiencing a changing magnetic field so current is induced.
When current is induced in a conductor a magnetic field is also induced, which reißt the magne falling down. Work is done by gravity against the magnetic field to produce the current, and it exits slowly
I think
How can the force on motor effect and current in generator effect increase
Motor
- increase magnetic flux
- increase length of wire
- increase current
- increase number of coils
Generators
- increase magnetic field (more field lines cut per second )
- increase coils / area of coils and more loops (more current induced in a loop so total increases)
- MOVE IT FASTER (more field lines cut per second
How else can you induce a current
4 ways
1) moving magnet in and out of coil
2) one coil is in circuit with dc power and is turned on and off next to a coil attached to a 0 sensitive ammeter. What happens here is when current given it induces a magnetic field which in turn induced a current in the second circuit. But when current removed the magnetic field still changes, stilk inducing current, gives ac for a second basically
3)moving coil in magnet, magnet is around coil
Using another coil that has alternating current in it . This is basically a transformer (induces changing magnetic field, produces changing current in second coil)
