Download Electromagnetic Induction

Electromagnetic
Induction
Making Electrical Current
Michael Faraday
• Faraday figured out that electrical current
moving through a wire created a magnetic
field.
• We made electromagnets!
• Faraday also figured out that moving a
magnetic field through electrical wires created
current.
• This is called induced current!
Induced Current
Electromotive Force
• Changing a magnetic field creates emf or
electromotive force.
• Faraday looked further into electromagnetic
induction.
• There was emf when a magnetic field was
moved through wires.
• There was also an emf when wires were
moved around a magnetic field.
• The motion only had to be relative for emf.
Motional EMF
• 𝜀 = 𝐵ℓ𝑣
• B is the magnetic field strength in teslas.
• ℓ is the length of the wire moving through the
field.
• v is the speed moving through the field in m/s.
• 𝜀 is in Volts.
• There must be motion for emf to be created!
Induced Current
Electromagnetic Flux
ΦB
Electromagnetic Flux
ΦB
ΦB = B⏊ A = B A cos θ
ΦB = magnetic flux
B⏊ = component of the magnetic field
perpendicular to loop of the wire.
A = area of the loop.
Electromagnetic Flux
ΦB
ΦB = B⏊ A = B A cos θ
B = strength of the magnetic field
A = area of the loop.
cos θ = angle of the magnetic field
to the surface of the loop.
Electromagnetic Flux
ΦB
ΦB = B⏊ A = B A cos θ
ΦB = tesla·meter2 = weber (Wb)
θ = 90°
Φ=0
θ = 45°
ΦB > 0
θ = 0°
ΦB = max
Faraday’s Law of Induction
• Electromotive Force (emf) is created by
moving an electromagnetic field through a
loop.
• The faster the ΦB is moved in a less amount of
time the more emf is created.
ℰ= ̶
ΔΦB
Δt
Lenz’s Law
• A current produced by an induced emf moves
in a direction so that its magnetic field
opposes the original change in flux.
• WARNING!!! CUIDADO!!!
• We are talking about two magnetic fields!!
• The magnetic field of the changing magnetic
flux!!
• The magnetic field of the induced current!!
Lenz’s
Law
Lenz’s Law
Lenz’s Law
Lenz’s Law
The End
Solenoids
Remember?
• A coil of wire with
electrical current running
through it is called a
solenoid.
• The magnetic field of each
loop adds to the magnetic
field of other loops.
• The South Pole is where
current flows in.
• The North Pole is where
the current flows out.
Magnitude of Magnetic Field
of a Solenoid interior.
B = μ0
NI
L
B is the magnetic field strength in teslas (T).
μ0 is the magnetic permeability of a vacuum.
μ0 = 4π × 10-7 N A-2
N is the number of turns in the wire.
I is the current in amperes (A).
L is the length of the solenoid.
Faraday’s Law of Induction
• If you add N loops the emf of each loop is
added together.
• The minus sign is to show us the direction of
the loop.
ΔΦB
ℰ= ̶ N
Δt
Generators
Generators
Generators
Generators
• Electrical current can be induced by spinning a
coil of wires inside a magnetic field.
• The reverse also works, a magnetic field can
be turned inside a coil of wires.
• Using steam to cause turbines to spin is the
basic idea of how all generators work.
• The only thing that changes is the energy
source to generate the steam (coal, gas,
nuclear, hydroelectric, solar, wind, etc.)
Generator Equation
ℰ = NBω A sin ωt
Generator Equation
ℰ = NBω A sin ωt
ℰ is electromotive force
N is number of turns in the wire.
B is magnetic field strength.
A is area of the loop.
ω is angular velocity in radians/s.
t is time.
Transformers
Transformers
Transformers
• Transformers are used to increase or decrease
voltage. (Technically AC voltage but we will get
to that later.)
• They have primary and secondary coils linked
by an iron core.
• Both the coils and the core are insulated to
guard against the effects of magnetic fields
(we will get to eddy currents later).
Transformers
• A step-down transformer has more primary
coil loops than secondary coil loops. The
voltage going out decreases.
• Np ˃ Ns
• A step-up transformer has more secondary
coil loops than primary coil loops. The voltage
going out increases.
• Ns ˃ Np
Transformers
Transformers
Transformers
Transformer Equation I
Vs
Ns
= N
Vp
p
Everything is insulated ΦB can be ignored.
Vp / Vs are voltage of primary and secondary
coils.
Np / Ns are the number of turns of primary and
secondary coils.
Transformer Equation II
Is
Ip
Np
= N
s
Everything is insulated ΦB can be ignored.
Ip / Is are current of primary and secondary coils.
Np / Ns are the number of turns of primary and
secondary coils.
The End