magnetic field and emf
Total emf for a coil
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There different steps to determine the induced current direction according to lenz's law
What is the change that is happening, what will oppose the change, what must the current direction be to match theis oposition.
Carbon brushes press against the slip rings the allow
a constant output to be transferred to a circuit without a fixed point of connection.
If magnet is quickly moved into a coil an emf is induced that causes
a current to flow in the complete circuit containing the coil.
A strong magnetic field acting over a small area can produce the same amount of magnetic flux as
a weaker field acting over a large area.
In a AC generator The resultant emf alternate in the direction
above and below the zero emf line.
Power distribution works on
alternating current
Magnetic flux
amount of magnetic field.
Lenz's law states that
an induced emf always gives rise to a current whose magnetic field will oppose the original change in flux.
Eddy current can be used to
apply a force that opposes the source of motion of an external agnetic field.
The magnetic flux will be a maximum when the
area examined is perpendicular to the magnetic field and zero when the area being examined is parallel to the magnetic field.
The iron core framework in the alternator is called the
armature
Faraday's law of induction.
average emf induced in a conducting loop in which there is a changing magnetic flux is proportional to the rate of change of flux.
A DC motor will also generate an emf called
back emf
Faraday law of induction is one of the
basic laws of electromagnetism.
A coil not connect to a circuit will act like a
battery not connected to a circuit. It will still have an induced emf but no current.
Lenz's law tells us that as the flux in the loop decreases from o to 90 the induced current will
be in a direction such as to create a agent field in the same dirction as the external field.
When using BAcostheta the angle is the angle
between a normal to the area and the direction of the magnetic field.
Induced emf can be created in three ways
by changing the strength of the magnetic field, changing the area of the coil within th magnetic field, changing the orientaion of the coil with respect to the direction of the magnetic field
An induced emf is created while there is a
change in flux
emf will be induced by a
change in magnetic field..
A transformer works on the principle that a
changing magnetic flux induces an emf.
The requirement for an induced emf is to have a
changing magnetic flux.
eddy currents
circular electric current induced within a conductor by changing magnetic field.
The dynamic microphone uses
coil attached to a diaphragm which vibrates with sound. The coil vibrates within the magnetic field of a permanent magnet thsu producing an induced emf that varies with the original sound.
DV voltage has a
constant unchanging current
To reduce eddy current loses in transformers the
core is made of laminations which are thin plates in iron electricity insulated from each other and placed so that the insulation between the laminations interupts the eddy currents.
Back omg in a DC motor is a result of
current produced in response to the motion of a conducting coil inside the motor in the prescence of an external magnetic field.
If the end of a coil are connected to an external circuit then
current will flow.
Emf is created when wires
cut across the magnetic field lines.
Emf is only generated where the sides are
cutting flux.
The step down transformer,
decreases the secondary emf compared with the primary emf
A transformer is a
device for increasing and decreasing ac voltage.
The value of the emf in the secondary coil will be
different and depends upon the number of turns in each coil.
Why AC is used in power distrubution?
ease with which AC is transformed from one voltage to another.
Induction hotplate heats via
eddy currents
The earth's magnetic field is also a result of
eddy currents
The use of AC as the standard for distribution allows highly
efficient and relatively cheap transformers to convert the initial volatges created at the power stations to much higher levels
Magnetic field should be able to to produce an
electric current
In a alternator mechanical energy is being transformed to
electrical energy and an emf is induced in a rotating coil.
During acceleration the car's system uses
electricity from the batter, converts it to voltage required via an inverter transformer and send it to the electric motor to power th car
Relative motion between a coil and a magnetic field induces an
emf
The current produced by a change in magnetic field is called
emf
The resulting output of all three phases in a three case generator maintains an
emf near the maximum voltage more continuously.
In three phase generator coils are arranged such that
emus vary and the same frequency , but peaks an troughs of their waveforms offset to provide three complementary currents with a phase sepration of one thrid pf a cycle.
If lens's law was not true then the new magnetic field creaed by a changing flux will
encourage that change adding energy into the universe.
In a duper conductor and induced current does not
fade away.
As the area of the coil decreases due to its changing shape the
flux through the coil also decreases.
Eddy currents produce their own magnetic field which contribute to the Earth's field and so a heat driven process called
geodynamo is created.
Although the transformer increase/decreases an AC emf the output power cannot be
greater than the input power
To transmit the same power as a DC system an AC system will have to operate with a
higher peak voltage.
If the magnet is removed then the current in the coil will flow
in the opposite direction.
A step up transformer
increases the secondary emf compared tot he primary emf.
Moving the magnet towards or away from the coil willl
induce an emf in the coil as there is a change in flux.
Change in the magnetic field when a magnet is moved closer to a conductor will lead to an
induced emf that produces an induced current in a complete circuit.
The greater the change in magnetic field the greater the
induced emf.
A generator is basically just the
inverse of a motor.
Regenerative breking overcomes the problem of
kinetic edgy being lost to heat when the car brakes and wasting fuel.
The net emf used by a dc motor is always
less than the applied voltage. E= V- Eback
Peak emf induced when the magnet first enters the coil at a relatively low speed is
less than the peak emf when the magnet leaves at a faster speed.
The challenge is to transmit large amount of power being produced at power stations using
low current
Induced emf will produce a current in the coil and this induced current will then produce its own
magnetic field that interacts with the permanent magnet to oppose its motion.
Applying lenz's law eddy current will be in a direction that creates a
magnetic field the opposes the change in magnetic flux that created it.
Magnetic field strength is also referred to as
magnetic flux density.
Its is the rate of change of
magnetic flux that induces emf.
An alternators (basic electric generator) consist of
many coils of wire wound on an iron core framework.
Many industrial applications require a more constant
maximum voltage than is possible from a single coil and require a three phase generator.
The axle is turned by
mechanical means
Lenz's law is important for applications such as
metal detectors and induction stoves.
Construction of an AC generator is basically the same as a
motor
B can be thought as being proportional to the
number of magnetic field lines per unit area perpendicular to the magnetic field.
applying lena'e law the magnetic field created by the induced current will
oppose the approaching field caused by the movement of the magnet.
Applying lens law to decrease in area decreasing flux, the direction of the induced curent will
oppose this change such the ist acts to increase the magnetic flux .
The back emf according to lenz's law
opposes the change in magnetic flux that created it so this induced emf will be in the opposite diretion to the applied emf creatg the motion in the first place.
zero emf occurs when the motion of the wires is
parallel to the field lines, 0, 180,360
Transformers are designed so nearly all the magnetic flux produced by the primary coil will
pass through the secondary coil.
maximum emf occurs when the wires cut the magnetic field
perpendicularly, 90, 270
Electric guitars use
picks that transform the mechanical energy of a vibrating guitar into electrical energy by the way of electomagnetic induction.
In a DC germinator the output can be smoothed by
placing a capacitor in parallel with the output or use of armature wiindings and more splits in commutator by ensuring output is always connected to an armature winding that s psoitioned to genrate maximum emf.
A transformer will consist of two coils called
primary and secondary coils.
Induced emf will be a maximum when the
rate of change of flux is a maximum.
As the angle increases and decreases from 90 the amount of magnetic flux will decrease until it
reaches zero, when the area is parallel to the magnetc field.
Regenerative breaking overcomes the problem by
recapturing much of the car's kinetic energy and converting it to electrical energy to recharge the car's battery.
Changing the orientation of a coil with in a magnetic field by rotating it will
reduce the amount of flux through the coil and so induces an emf in the coil while its being rotated.
In many industrial generators the coils
remain static and the electromagnets rotates within them
Over large distance even relatively good conductors have a significant
resistance
Superconductivity describes the phenomenon of
resistance of metals decreasing when they cooled.
The regenerative braking system runs the car's electric motor in
reverse converting mechanical energy into electrical energy and then into car battery storage.
During breaking the process is
reversed.
The split ring means the
ring pricing up the output from he coil has two breaks in oppsite sides.
The armature is made to
rotate in a magnetic field.
Considering a single loop in a generator, the loop is
rotated clockwise in a uniform magnetic field and the amount of flux threading through the loop varies inducing the emf.
In small generators the coils are
rotated within a magnetic field
An AC generator produces an alternating current that varies
sinusoidally over time with the change in magnetic flux.
Output from the coil is transferred to a circuit via continuous
slip rings, the alternating current will be maintained at the ouput.
In a DC generator the continuous slip ring is replaced by a
split ring commutator.
In large power stations, car alternators etc the coils are
stationary and an electromagnet rotates them
Superconductivity has to do with the magnetic properties of the
superconductor.
The slip rings allow
the coil to rotate without tangling the connecting wires.
Tranformers do not work with
the constant current of a DC electrical supply.
Lenz's law is an necessary consequence of
the law of conservation of energy.
From faraway law, the average emf in the primary coil will affect the rate at which
the magnetic flux changes.
The direction of output is changed by the split ring commutator every half turn so that
the output current is always in the same direction.
t=The direction of the induced current will reverse every time
the plane of the reaches point perpendicular to the field,
The magnitude of the induced emf will be determined by
the rate at which the loop is rotating.
Electromagnetic induction
the reaction of an electric current in a conductor due to change in the magnetic field acting on that conductor
In a transformer The changing flux originates from the alternating current supplied to the primary coil and is directed to
the secondary cil where the changing flux will induce an emf in that coil.
A change can be created by any method that causes a change in
the strength of magnetic field or afea of the coil perpendicular to the magnetic field
Magnetic flux is defined as the product of
the strength of the magnetic field , B, and area of the field perpendicular.
I n an ideal transformer the assumption is that
the transfer of magnetic flux is 100% efficient and energy losses are ignored.
The magnitude of emf on each side can be expressed as
the velocity of the loop perpendicular to the magnetic field.
Faraway was not able to produce an electric current when he used a constant magentic field but was able to create an electric current when
there was a change in magnetic field.
A transformer will be overloaded if
too much current is drawn and the resistive power loss it he wires becomes too great.
Transformers are a common solution to the challenge of
transmitting power with low current.
Emf can also be induced by changing
A, the area perpendicular to the magnet field and through which the magnetic field lines pass, while keeping B constant.
How the AC in the coil is harnessed determines if the device is
AC alternator or DC generator.
When an AC emf is connected to the primary coil of a transformer the changing magnetic field will induce a
AC emf in the secondary coil of the same frequency as the primary emf.
A DC generator is much like an
AC generator
The principle of an electric power generator is the same whether the result is
AC/DC
Lenz's law is a common way of
understanding how electromagnetic induction obeys the priciples of conservation of energy and explains the direction of induced emf.
With a commutator the output will still
vary from zero the maximum every half cycle
transmitting large amount of power using a large current will create
very large power loss
The average power can be obtained by using a value for the
voltage and current equal to the peak values and dividing it by square root of 2.
emf
voltage/potential difference
Negative sign before fairways law is there to remind you
which direction the induced emf acts. (which direction current flows as a result of the induce emf)
It is a maxim When the loop is moving through a position parallel to the magnetic field where the flux through the loop is
zero
How induction hot plates work?
Ac electricity supply produce changing magnetic field in the coil. This induces an eddy current i the conductive metal pot. The resistance of the metal in the pot, in which the eddy current flows, transform electrical energy into energy into heat and cooks
How is earth's field from eddy currents?
Radioactive decay in earth's core produces heat. covention in molten acts like spinning discs hence moving the earth's magnetic field inducing eddy currents.
Magnetic levitation
Resultant field opposes the changing the changing flux and magnet is repelled.
Standby power can add up to around
10% of standby power
