Magnetic Induction

Question 1

______________ 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 ____________

Answer 1

Electromagnetic
induction
electromagnetic induction

Question 2

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

Answer 2

Oersted
Faraday

Question 3

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.

Answer 3

deflections
no deflections
change

greater
decreases

Question 4

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.

Answer 4

Faraday
a coil of wire, galvanometer, and a bar magnet,

Question 5

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

Answer 5

similar manner

Question 6

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 _________.

Answer 6

constant
flux meter
weber (Wb)
Maxwell.

Question 7

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.

Answer 7

Faraday’s Law

Neumann’s Law

Lenz’s Law

Question 8

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.

Answer 8

Lenz’s law

Question 9

 __________ 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.

Answer 9

Self-Induction
decay
growth

Question 10

 ____________ 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.

Answer 10

Mutual induction

opposes the decay

opposes the growth

Question 11

 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.

Answer 11

transformer

either

Question 12

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

Answer 12

electric charge
magnetic field
electric field
magnetic induction

Question 13

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 __________

Answer 13

Orsted in 1820
electric current
electric field
magnetic field
Michael Faraday

Question 14

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 __________

Answer 14

induced electric field
ammeter
current
both zero

Question 15

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 ________

Answer 15

no current
light up

Question 16

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 ______________

Answer 16

electric current
wire loop

electric field
induced electric field
electromagnetic induction

Question 17

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

Answer 17

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)

Question 18

_____________ indicates how to calculate the potential difference that produces the
induced current

Answer 18

Faraday’s Law

Question 19

The magnitude of the induced emf equals the rate of change of the _________
 The negative sign is __________

Answer 19

magnetic flux
Lenz’s Law

Question 20

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 ______

Answer 20

&
voltmeter
current

Question 21

The emf is produced by changes in the _________ through the circuit
 A constant flux does not produce an induced voltage

Answer 21

magnetic flux

Question 22

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

Answer 22

magnetic field
area
angle
voltmeter

Question 23

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

Answer 23

magnetic flux
larger values
frequency

magnitude
emf
present

Question 24

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

Answer 24

magnetic field
constant
magnitude of induced emf
power dissipation

Question 25

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 __________________

Answer 25

equal
mechanical to electrical, same
electromagnetic phenomena

Question 26

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

Answer 26

rate of change of the flux
rotational motion
constant magnetic field

Question 27

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

Answer 27

wire loop
loop
rotates

sinusoidally
70 V

Question 28

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

Answer 28

magnitude of the magnetic field
area
loop rotates
one region to another

Question 29

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.

Answer 29

induced emf
opposes
perimeter

Question 30

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.

Answer 30

negative sign
conservation of energy
Faraday’s Law

Question 31

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 ______.

Answer 31

induced flux
current
magnetic field.
coil

Question 32

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

Answer 32

coil
small solenoid
inductor
voltage

self-inductance
current
opposes

Question 33

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 ___________

Answer 33

inductance of a solenoid
L
inductance

Question 34

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

Answer 34

induced current
indirectly through

Question 35

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 _______

Answer 35

battery
equal
zero

Question 36

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