Magnetic Induction Flashcards by Nicholae C. SARA

______________ 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

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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

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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

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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,

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The flux of the magnetic field through a surface is defined in a _________ as we
defined flux in the electric field.

similar manner

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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.

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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

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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

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 __________ 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

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 ____________ 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

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 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

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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

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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

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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

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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

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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