electromagnetic induction
Download
Skip this Video
Download Presentation
Electromagnetic Induction

Loading in 2 Seconds...

play fullscreen
1 / 29

Electromagnetic Induction - PowerPoint PPT Presentation


  • 100 Views
  • Uploaded on

Electromagnetic Induction. What’s Next?. Electromagnetic Induction Faraday’s Discovery Electromotive Force Magnetic Flux Electric Generators Lenz’s Law Self-Inductance Transformers. What do we know?. Hans Christian Oersted showed that moving charges create a magnetic field.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Electromagnetic Induction' - kyleigh-dallaher


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
what s next
What’s Next?
  • Electromagnetic Induction
  • Faraday’s Discovery
  • Electromotive Force
  • Magnetic Flux
  • Electric Generators
  • Lenz’s Law
  • Self-Inductance
  • Transformers
what do we know
What do we know?
  • Hans Christian Oersted showed that moving charges create a magnetic field.
faraday s hypothesis
Faraday’s Hypothesis
  • If moving charges produced a magnetic field, could a moving or changing magnetic field produce a current?
faraday s discovery
Faraday’s Discovery
  • Faraday discovered that he could induce current by moving a wire loop through a magnetic field or moving the magnetic field through a wire loop.
  • Faraday’s Discovery is known as Electromagnetic Induction
  • Faraday's Discovery
electromotive force
x x x x x x x x x

x x x x x x x x x

x x x x x x x x x

+

-

L

v

F

Electromotive Force
  • Last week we learned the Lorentz Force.

FB = qvB sinθ = BIL sinθ

  • When a conductor moves through a magnetic field, a force is exerted on these charges causing them to separate, inducing an EMF.
electromotive force1
Electromotive Force
  • We know: W = Fd and V = W/q.

V = Fd/q

Using algebra and solving for F:

F = Vq/d

F = qvB

Set these two relationships equal to one another and then solve for V, which will now be represented as EMF:

EMF (V) = vBL

Where: L is the length of a conductor passing through a magnetic field.

EMF = Electromotive Force (Volts)

electromotive force2
I

+

x x x x x x x x x

x x x x x x x x x

x x x x x x x x x

x x x x x x x x x

I

F

v

-

Electromotive Force
  • The EMF results when the conductor has a velocity component perpendicular to the magnetic field.
  • Use RHR #1 where the thumb points in the direction of the velocity. The force on the bar is opposite the velocity.

I

example 1 em induction
Example 1: EM Induction

A segment of a wire loop is moving downward through the poles of a magnet, as shown. What is the direction of the induced current?

a. The current direction is out-of the page to the left.

b. There is no induced current.

c. The current direction is into the page to the right.

example 2 em induction
Example 2: EM Induction
  • The drawing shows three identical rods (A, B, and C) moving in different planes in a constant magnetic field directed along the +y axis. The length of each rod and the speeds are the same, vA = vB = vC. Which end (1 or 2) of each rod is positive?
  • Rod A:
    • 1 b. 2 c. neither
  • Rod B:
    • 1 b. 2 c. neither
  • Rod C:
    • 1 b. 2 c. neither
electromagnetic induction1
Electromagnetic Induction
  • Why is it important?
    • Motors
    • Generators
    • Transformers
electric generators
Electric Generators
  • Invented by Michael Faraday.
  • Convert mechanical energy into electrical energy.
  • Similar to an electric motor, but function in an opposite manner.
  • Electrical power generation is the foundation by which electricity is supplied to homes and businesses around the world.
  • Electricity is generated in many ways - hydroelectric, nuclear, coal, gas, oil fired, wind solar, geothermal.
magnetic flux
Magnetic Flux

What is magnetic flux?

  • Like electric flux
  • A measure of the strength of the magnetic field, B, passing through a surface perpendicular to the field.
  • For a bar magnet, the flux is maximum at the poles.
  • The more magnetic field lines, the higher the flux.

=BAcos

magnetic flux and emf
Magnetic Flux and EMF
  • We already know:

EMF = vBL

  • v = Δx/Δt = (x – xo)

(t – to)

  • EMF = (Δx/Δt)BL = (xL – xoL) B = (BA) – (BAo)

(t – to) (t – to)

EMF = -ΔΦ/Δt Where:

 = BA cos and

      • = the angle the normal

to the surface makes

with B (in this drawing it

is 0o).

I

+

x x x x x x

x x x x x x

x x x x x x

x x x x x x

F

I

v

-

faraday s law of em induction
Faraday’s Law of EM Induction
  • In the drawing on the previous slide, there is only one loop in the circuit.
  • When there is more than one loop in a circuit, as in the coil of a solenoid, the EMF induced by a changing magnetic field will increase by a factor equal to the number of loops in the coil.

EMF = -N ΔΦ/Δt

Where N = the number of loops in the coil.

  • Note: The units for Φ are Webers (Wb) or 1 Tm2
magnetic flux generators

I

x

x

x

Magnetic Flux & Generators

Direction of Rotation

v

v

v

w

B

v

v

v

Zero Current

Min Change in Flux

Max Current

Max Change in Flux

Axis of Rotation

magnetic flux generators1
Magnetic Flux & Generators
  • When the armature is at 90o with the magnetic field, the current will be zero because the rate of change in magnetic flux through the coil will be at a minimum.
  • When the windings of the armature are aligned with the direction of the magnetic field, the current will be at a maximum because the rate of change in magnetic flux will be at a maximum.
principle operation and characteristics of a generator
Principle Operation and Characteristics of a Generator
  • The armature turns such that the coils of wire cut through the magnetic field inducing an EMF in the coil.
  • The magnetic field or the conductor need to be moving in order for an EMF to be generated.
  • The greater the change in magnetic field, the greater the EMF, ie. the faster the armature turns, the greater the power produced.
  • Use RHR #1 to determine the direction of current through the coil.
  • Generator
lenz s law
Lenz’s Law
  • The induced EMF resulting from a changing magnetic flux has a polarity that leads to an induced current whose direction is such that the induced magnetic field opposes the original flux change.
    • If the magnetic field is increasing, a current will develop to oppose the increasing magnetic field.
    • If the magnetic field is decreasing, a current will develop to create a magnetic field in the same direction as the one that is decreasing.
    • A current will form that attempts to keep the magnetic field constant.
    • Lenz’s Law abides by the laws of conservation of energy.
lenz s law1
Lenz’s Law

Lenz's Law

lenz s law2
No Current

Induced

Current

x x x x x x

x x x x x x

x x x x x x

x x x x x x

No Current

Induced

Current

No Current

Lenz’s Law

Current will be induced in the copper ring when it passes through a region where the magnetic field changes. When the magnetic field is constant or absent, their will be no induced current.

applications of lenz s law eddy currents
Applications of Lenz’s Law (Eddy Currents)
  • Eddy current balances.
  • Eddy current dynamometer.
  • Metal detectors (Lenz's Law)
  • Braking systems on trains.
  • What are Eddy currents?
    • Eddy currents are currents created in conductors to oppose the changing magnetic fields they are exposed to.
    • Eddy currents respond to the changes in an external magnetic field.
    • Eddy currents can form in conductors even if they are not capable of being magnetized.
lenz s law and motors back emf
Lenz’s Law and Motors – Back EMF
  • When a current carrying wire moves in a magnetic field, an EMF is produced called the back EMF.
  • The back EMF opposes the current in the motor resulting in a decrease in the total current through the motor.
  • As the motor slows down, the current will increase.
  • Back EMF’s may cause sparks at outlets and switches when circuits are disconnected while in use.
back emf in electric motors
Back EMF in Electric Motors
  • Both motors and generators consist of coils that rotate in a magnetic field.
    • There are two sources of EMF:
      • An applied EMF to drive the motor.
      • An EMF induced (back EMF) by the generator like action of the coil that opposes the applied EMF.

EMFnet = Vapplied – EMFinduced

I = (Vapplied – EMFinduced)/R

transformers
Transformers
  • Transformers are used to increase or decrease AC voltage.
    • Transformers that increase voltage are called step-up transformers.
    • Transformers that decrease voltage are called step-down transformers.
  • Transformers efficiently change voltages with little loss of energy.
transformer design
Transformer Design
  • Transformers consist of two windings wrapped around an iron core.
  • The iron core is easily magnetized and will enhance the magnetic field.
  • Mutual Inductance: The changing current in one coil (primary) will induce an EMF in the other coil (secondary).
transformers cont
Power losses are minimal for transformersTransformers (cont.)
  • The EMF induced (secondary voltage, Vs) in a secondary coil is proportional to the primary voltage (Vp).
  • The EMF induced is also proportional to the number of windings (Ns) in the secondary coil.
  • The EMF is inversely proportional to the number of windings in the primary coil (Np).

Vs/Vp = Ns/Np

Pp = Ps

VpIp = VsIs

Rearranging: Is/Ip = Vp/Vs = Np/Ns

key ideas
Key Ideas
  • Electromagnetic induction: is the process by which current is generated by moving a conductor through a magnetic field or a magnetic field through a conductor.
  • The induced current is maximum when the relative motion of the conductor is perpendicular to the magnetic field.
  • The induced voltage is called EMF (=vBL).
  • Magnetic flux is a measure of the strength of the magnetic field passing through a surface.
  • A generator is a device that converts mechanical energy into electrical energy.
  • Generators are similar to motors.
key ideas1
Key Ideas
  • Lenz’s Law: The induced EMF resulting from a changing magnetic flux has a polarity that leads to an induced current whose direction is such that the induced magnetic field opposes the original flux change.
  • Self-Inductance: A changing current in a coil will induce an EMF that opposes the change in current.
  • Transformers convert high voltage/low current electrical energy to low voltage/high current electrical energy.
  • Transformers consist of two coils (primary and secondary) wrapped around a common iron core.
ad