If an electric current can produce a magnetic field,

can a magnetic field would induce an electric current ?

yes,

Almost 200 years ago, Faraday found evidence

a current that is produced due to a changing magnetic field.

therefore we can say a changing magnetic field induces an emf (e.g. a battery).

this phenomenon is called electromagentic induction.

Faraday's experiments with a magnet &  a coil:

What happens when the magnet moves up toward the coil:

Is there a current produced?

Is the magentic field increasing or decreasing in the coil?

A current is induced.

Magnetic field in the coil is increasing.

Faraday's experiments with a magnet &  a coil:

What happens when the magnet moves down ,away, from the coil:

Is there a current produced?

Is the magentic field increasing or decreasing in the coil?

A current is induced in the opposite direction.

The magnetic field in the coil decreases.

Faraday's experiments with a magnet &  a coil:

What happens when the magnet is held steady and the

coil is moved toward/away the magnet:

Is there a current induced?

Is the magentic field increasing or decreasing in the coil?

Yes a current is still induced.

It doesnt matter whether the coil or the magnet moves, 

motion or change is required to induce an emf. So it is the realtive motion btwn the magnet & coil that is important.

the magnetic field in coil is constant.

the more rapidly the magnetic field changes the ____ (greater,lesser) the induced emf will  be in a loop of a wire

The induced emf in a wire loop is :

inversely proportional/ proportional

to the rate of change of magnetic flux through the loop.

write the formula for:

 magnetic flux for a uniform magnetic field through a loop of area(A)

ΦB=

ΦB= BAcosθ

where:

B is the component of the magnetic field perpendicular to loop

θ: is the angle btwn B & a line perpendicular to the face  of the loop.

when the face of the loop is parallel to B,

θ?

ΦB (magnetic flux)?

θ= 90

ΦB (magnetic flux) = 0

b/c cos 90=0

when the face of the loop is perpendicular to B,

θ?

ΦB (magnetic flux)?

θ:0

ΦB (magnetic flux): BA

(magentic field in Telsa's * area in m²)

weber, Wb.

1 Wb = 1 T·m2

it is proportional to the total number of lines passing through the loop.

Faraday's law of induction says for 1 loop:

 the induced emf E is proportional to ____and inversely proportional to

proportional to: net change in magentic flux ΔΦ_B

inversely proportional to: change in time Δt

Faraday's law of induction says for N loops:

 the induced emf E is proportional to ____

& inversely proportional to ______

Note the emf in each loops are added together

proportional to: net change in magentic flux ΔΦ_B

inversely proportional to: change in time Δt

A current produced by an induced emf moves in a direction

so that the magnetic field it produces tends to restore the changed field.

(1) the changing magnetic field or flux that induces the current

(2) the magnetic field produced by the induced current (note all currents produces an electric field)

the 2nd field opposses the 1st field.

the changing flux through the coil

induces an emf through the coil

= 

a current is produced

=

this induced current produces its own magentic field

apply lenz's law to a coil & a magnet:

if the distance btwn the coil & the magnet decreases (aka they got CLOSER) :

1.the magnet's magnetic field (aka the # of field lines through the coil) will increase/decrease?

2. causes the magnetic flux to increase or decrease?

1. mag. field: increases

2.mag. flux: increases

apply lenz's law to a coil & a magnet:

if the distance btwn the coil & the magnet increases (aka they get FURTHER APART) :

1.the magnet's magnetic field (aka the # of field lines through the coil) will increase/decrease?

2. causes the magnetic flux to increase or decrease?

1. mag field: decreases

2. mag flux: decreases

Since magnetic flux:

Φ_{B =} BAcosθ

an emf can be induced in what 3 ways?

1. by changing the magnetic field

2. by the changing the area  (A) of loop inside the field

3. by changing the loop's orientation (the angle θ) with respect to the field.

the AC current sets up a changing magentic    field that passes through the pan bottom

this changing magnectic field induces a current in the pan bottom

However a metal pan has little resistance = electrical energy is converted to thermal energy

a glass container has a high resistance=

little current induced=

little energy is transferred to container

true or false:

an electric field will be induced at any in space where there is a changing magnetic field.

if 2 coils of a wire are near each other, a changing current in one coil will induce an emf in the other.

 is an example of _______ inductance?

 mutual inductance

For example: the change in the  emf induced in coil 2 is produced by the changing current in coil 1 (aka the rate of change of flux passing through it).

V *s /A 

=

Ω *s

=

1 Henry

mutual inductance (M)

1.what doesnt depend on?

2.what does it depend on?

M is a" constant"

does not depend on: current of coil 1 (I₁)  (the coil who is doing the inducing to the other coil)

depends on: geometric factors

size

shape

# of turns

realtive position of the 2 coils

whether or not iron (or any ferromagnetic material is present).

mutual inductance:

↑ distance btwn coil 1 &2

means

_____ lines of flux can pass through coil 2

M will be _____

↓ lines of flux can pass through coil 2

M will be ↓

(aka think the farther they are apart the less it can be induced)

opposses 

(follows Lenz's law)

self inductance ( the constant L) is units of ?

depends on (3)?

henry (Ω*s)

size,shape of coil 

& prescense of an iron core.