Magnetic Induction Flashcards
______________ refers to the generation of an electric current by passing a metal wire through a magnetic field.
_________________ is the production of an electromotive force across an electrical conductor in a changing magnetic field.
When an induced current is produced because of voltage production (E.M.F) due to a changing magnetic field, it is called ____________
Electromagnetic
induction
electromagnetic induction
Brief History of Electromagnetic Induction
In 1820, ______ first discovered that a magnetic field is always associated with an
electric current.
In 1831, August 29, _________ discovered electromagnetic
Oersted
Faraday
Characteristics of Electromagnetic Induction
For movements between magnetic bar and the conductor, there will be ____________ in
galvanometer.
If the bar and the conductor remain steady then there will be __________ in the
galvanometer.
If the pole of the magnetic bar is changed, the direction of induced current will ________.
When the loops in the coil increases the deflection become _____ and when loops
_________ the deflection become smaller.
deflections
no deflections
change
greater
decreases
Faraday’s experiments of Electromagnetic Induction
________ conducted three different experiments to find electromagnetic induction.
He used a ______, _________ and _________, by noticing deflections he
conducted his first experiment.
He replaced the magnet bar with a current carrying solenoid to perform his second
experiment.
He placed two coils close together face to face but at rest with respect to each other and
by closing and opening the circuit he conducted his third experiment.
Faraday
a coil of wire, galvanometer, and a bar magnet,
The flux of the magnetic field through a surface is defined in a _________ as we
defined flux in the electric field.
similar manner
Magnetic Flux
If the magnetic field is __________, the magnetic flux passing through a surface of vector area S is ∅B= B.S cos θ
Magnetic flux is usually measured with a _________, which contains measuring coils and electronics that evaluates the change of voltage in the measuring coils to calculate the magnetic flux.
The SI unit of magnetic flux is the ________ (in derived units: volt seconds), and the CGS unit is the _________.
constant
flux meter
weber (Wb)
Maxwell.
Laws of Electromagnetic Induction
________: It states that, the E.M.F induced in a wire is proportional to the rate of the flux through the loop.
____________: The magnitude of the induced E.M.F is proportional to the rate of change of the magnetic flux linking the circuit.
__________: The induced E.M.F acts to the circulate a current in a direction that oppose the change in flux which caused the induced E.M.F.
Faraday’s Law
Neumann’s Law
Lenz’s Law
Explanation
According to _________, the direction of included current in a coil is such that it always
opposes the cause which produces it.
This law follows the law of conservation of energy.
Lenz’s law
__________ is the characteristic of the coil itself.
When the main current in the coil decreases, the induced current opposes the _______ of
current in the coil.
When the main current in the coil increases, the induced current opposes the ________ of
current in the coil.
Self-Induction
decay
growth
____________ is the characteristic of a pair of coils.
When the main current in the coil decreases, induced current developed in the
neighbouring coil ______________ of current in the coil.
When the main current in the coil increases, the induced current developed in the
neighbouring coil ______________ of current in the coil.
Mutual induction
opposes the decay
opposes the growth
A _____________ is an electrical device which, by the principles of electromagnetic
induction.
It transfers electrical energy from one electric circuit to another, without changing the
frequency.
Transformers ________ increases or decreases AC voltage, two types step-up and step-
down.
transformer
either
Magnetic Induction
Electric and magnetic forces both act only on particles carrying an _________
Moving electric charges create a __________
A changing magnetic field creates an _____________.
- This effect is called __________
- This links electricity and magnetism in a fundamental way
Magnetic induction is also the key to many practical applications
electric charge
magnetic field
electric field
magnetic induction
Electromagnetism
Electric and magnetic phenomena were connected by _________
- He discovered an ____________ in a wire can exert a force on a compass
needle
- Indicated a _________ can lead to a force on a magnet
- He concluded an electric field can produce a __________
Did a magnetic field produce an electric field?
- Experiments were done by __________
Orsted in 1820
electric current
electric field
magnetic field
Michael Faraday
Faraday’s Experiment
Faraday attempted to observe an ___________
He used an ____________ instead of a light bulb
If the bar magnet was in motion, a ______ was observed
If the magnet is stationary, the current and the electric field are __________
induced electric field
ammeter
current
both zero
Another Faraday Experiment
A solenoid is positioned near a loop of wire with the light bulb
He passed a current through the solenoid by connecting it to a battery
When the current through the solenoid is constant, there is ___________ in the wire
When the switch is opened or closed, the bulb does ________
no current
light up
Conclusions from Experiments
An ___________ is produced during those instances when the current through the
solenoid is changing
Faraday’s experiments show that an electric current is produced in the___________ only
when the magnetic field at the loop is changing
A changing magnetic field produces an ________
- An electric field produced in this way is called an ___________
- The phenomena is called ______________
electric current
wire loop
electric field
induced electric field
electromagnetic induction
Magnetic Flux
Faraday developed a quantitative theory of induction now called __________
- The law shows how to calculate the induced electric field in different situations
Faraday’s Law uses the concept of __________
- Magnetic flux is similar to the concept of electric flux
Let A be an area of a surface with a magnetic field passing through it
The flux is _________
If the field is perpendicular to the surface, ________
If the field makes an angle with the normal to the surface, _________
If the field is parallel to the surface, _________
The magnetic flux can be defined for any surface
- A complicated surface can be broken into small regions and the definition of flux
applied
- The total flux is the sum of the fluxes through all the individual pieces of the
surface.
The surfaces of interest are _________
With electric flux, ___________ were used
The SI unit of magnetic flux is the _______
1 Wb=1 T x m2
Faraday’s Law
magnetic flux
∅B= B.A cos θ
∅B= BA
∅B= B.A cos θ
∅B= 0
open surfaces
closed surfaces
Weber(Wb)
_____________ indicates how to calculate the potential difference that produces the
induced current
Faraday’s Law
The magnitude of the induced emf equals the rate of change of the _________
The negative sign is __________
magnetic flux
Lenz’s Law
The ___ is the induced emf in the wire loop
Its value will be indicated on the ________
It is related to the electric field directly along and inside the wire loop
The induced potential difference produces the ______
&
voltmeter
current
The emf is produced by changes in the _________ through the circuit
A constant flux does not produce an induced voltage
magnetic flux
The flux can change due to
Changes in the _____________
Changes in the ________
Changes in the ___________
The___________ will indicate the direction of the induced emf and induced current
and electric field
magnetic field
area
angle
voltmeter
Faraday’s Law, Summary
Only changes in the ___________ matter
Rapid changes in the flux produce _______ of emf than do slow changes
This dependency on ________ means the induced emf plays an
important role in AC circuits
The _________ of the emf is proportional to the rate of change of the flux
- If the rate is constant, then the _____ is constant
- In most cases, this isn’t possible and AC currents result
The induced emf is _______ even if there is no current in the path enclosing an
area of changing magnetic flux
magnetic flux
larger values
frequency
magnitude
emf
present
Flux Through a Changing Area
A _________ is constant and in a direction perpendicular to the plane of the rails and
the bar
Assume the bar moves at a ______ speed
The ___________ is ε = BLV
The current leads to ___________ in the circuit
magnetic field
constant
magnitude of induced emf
power dissipation
Conservation of Energy
The mechanical power put into the bar by the external agent is _____ to the electrical
power delivered to the resistor
Energy is converted from __________, but the total energy remains the ____
Conservation of energy is obeyed by __________________
equal
mechanical to electrical, same
electromagnetic phenomena
Electrical Generator
Need to make the _____________ large enough to give a useful emf
Use _____________ instead of linear motion
A permanent magnet produces a _____________ in the region between its poles
rate of change of the flux
rotational motion
constant magnetic field
Generator, cont.
A ________ is located in the region of the field
The________ has a fixed area, but is mounted on a rotating shaft
The angle between the field and the plane of the loop changes as the loop _________
If the shaft rotates with a constant angular velocity, the flux varies ________
with time
This basic design could generate about _____ so it is a practical design
wire loop
loop
rotates
sinusoidally
70 V
Changing a Magnetic Flux, Summary
A change in magnetic flux and therefore an induced current can be produced in four
ways
If the ____________ changes with time
If the ______ changes with time
If the _______ so that the angle changes with time
If the loop moves from___________ and the magnitude of the field is
different in the two regions
magnitude of the magnetic field
area
loop rotates
one region to another
Lenz’s Law
Lenz’s Law gives an easy way to determine the sign of the ___________
Lenz’s Law states the magnetic field produced by an induced current always ____________
any changes in the magnetic flux
The induced emf is directed along the _________ of the flux surface. The induced current
is thus perpendicular to B.
induced emf
opposes
perimeter
Lenz’s Law and Conservation of Energy
Mathematically, Lenz’s Law is just the __________ in Faraday’s Law
It is actually a consequence of ______________
Therefore, conservation of energy is contained in _____________
Nowhere in the laws of electricity and magnetism is there any explicit mention of
energy or conservation of energy
Physicists believe all laws of physics must satisfy the principle of conservation of energy.
negative sign
conservation of energy
Faraday’s Law
Inductance
In some cases, you must include the ________
When the switch is closed, a sudden change in ________ occurs in the coil
This current produces a ___________.
An emf and current are induced in the ______.
induced flux
current
magnetic field.
coil
Inductor
A ________ is type of circuit element called an inductor
Many inductors are constructed as ___________.
Almost any coil or loop will act as an _____________
Whenever the current through an inductor changes, a _________ is induced in the inductor
that opposes this change
This phenomenon is called _________.
The current changing through a coil induces a _________ in the same coil
The induced current _________ the original applied current, from Lenz’s Law
coil
small solenoid
inductor
voltage
self-inductance
current
opposes
Inductance of a Solenoid
Faraday’s Law can be used to find the _______________
______ is the symbol for inductance
The voltage across the solenoid can be expressed in terms of the ___________
inductance of a solenoid
L
inductance
Mutual Inductance
It is possible for the magnetic field of one coil to produce an __________ in a second
coil
The coils are connected _______ the magnetic flux
induced current
indirectly through
RL Circuit
DC circuits may contain resistors, inductors, and capacitors
The voltage source is a _________ or some other source that provides a constant voltage across its output terminals
Behavior of DC circuits with inductors
Immediately after any switch is closed or opened, the induced emfs keep the
current through all inductors ______ to the values they had the instant before the
switch was thrown
After a switch has been closed or opened for a very long time, the induced emfs are _______
battery
equal
zero
Time Constant for RL Circuit
The current at time t is found by
_____ is called the time constant of the circuit
For a single resistor in series with a single inductor, T = L/R
The voltage is given by
