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Electromagnetic Induction Physics 30S

Physics 30S. A changing magnetic field creates an electric field A changing electric field creates a magnetic field Basis for electricity generation,

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Page 1: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Electromagnetic Induction

Physics 30S

Page 2: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Electromagnetism

Page 3: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

What is Electromagnetism?

A changing magnetic field creates an electric field

A changing electric field creates a magnetic field

Basis for electricity generation, transmission, most uses and applications

Page 4: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Maxwell’s Equations

Complicated, but in essence:

Electric fields and magnetic fields are one phenomena: an electromagnetic field

United concepts of electricity and magnetism into 4 equations

James Clerk MaxwellJune 13 ,1831 – November 5, 1879

Page 5: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Michael Faraday

Faraday was a great researcher

Intuitive knowledge about electricity and magnetism

Performed many experiments which paved the way for an understanding of electromagnetism Primitive motor

September 22, 1791 – August 25, 1867

Page 6: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Hans Christian Oersted

Oersted made one of the first electricity/magnetism insights all because of a messy desk

Current carrying wire caused compass needles to divert

Oersted’s basic principle of electromagnetism: moving electric charges produce a magnetic field

August 14,1777 – March 9, 1851

Page 7: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Field around a Current Carrying Wire

Current through a wire creates a circular magnetic field; weakens with distance

Right Hand Rule 1: Point thumb in the direction of the

current Make a fist Fingers show direction of magnetic field

Magnitude of field:B is the magnetic field (T)I is the current (A)r is the distance from the wire (m)

Page 8: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Right Hand Rule 1

Point your thumb in the direction of current flow

Fingers wrap to show direction of the magnetic field

Page 9: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Visualizing the Magnetic Field around a Wire

Point your thumb with the current

Curl your fingers to determine the direction of the field

Page 10: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

What is ?

Permeability of free space4π x 10-7 Tm/APhysical constantPermeability relates the ability of the

medium to induce a magnetic field Inductance

Page 11: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Notation

Current Coming out of the screen

Going into the screen

Meant to visualize an arrow

Page 12: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Example1 Right Hand Rule 1Add arrows to show the direction of

the magnetic field

Page 13: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Solution

Page 14: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Example 1: Calculating Field

a) What is the strength of the magnetic field 15 cm away from a wire carrying 75 A?B = 1.0 x 10-4 T

b) At what distance is the strength of the magnetic field 1.5 x 10-5 T?r = 1.0 m

Page 15: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Example 2: Calculating Field

a) How much current is a wire carrying if the magnetic field is measured to be 3.03 x 10-3 T at 0.500 meters away?I = 7580 A

b) What is the strength of the magnetic field 1.50 m from the wire?B = 1.01 x10-3 T

Page 16: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Homework

3. Magnetic Fields Homework Handout

Page 17: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Force on a Current Carrying Wire Current carrying wires experience a force

in an external magnetic field Right Hand Rule 2:

Make an L shape with your hand Thumb points in the direction of the current Fingers point in the direction of the magnetic

field Palm shows the direction of the force

Magnitude of the Force:B is the magnetic field (T)I is the current (A)l is the length of the wire (m)Θ is the angle between the magnetic field and the wire (not in the text)

Page 18: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Example 1 Right Hand Rule 2

What direction is the force on the wire?

Solution: Into the screen

Page 19: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Example 1: Calculating Force

A 25cm wire in a motor carrying 15 A of current is in a magnetic field of 0.2T. What will be the force on the wire, assuming that the wire and magnetic field are perpendicular?

FB = 0.08 N

Page 20: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Example 2: Calculating Force

What length of conductor, running at right angles to a 0.033 T magnetic field and carrying a current of 20.0 A, will experience a force of 0.10N?

I = 0.15 m

Page 21: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

What about Charged Particles? Magnetic fields exert a force on moving

electrical charges, including charged particles What might the formula be?

Page 22: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Example 1: Moving Particles

An electron is shot through a cathode ray tube TV at 5.0 x 105 m/s, perpendicular to the direction of the field. If the force acting on the particle is 2.0 x 10-15 N and the length of the tube is 10 cm, what is the strength of the magnetic field?

B = 0.025 T

Page 23: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Example 2: Moving Particles

An alpha particle (He2+) is shot through a magnetic field at 3.33 x 106 m/s, perpendicular to the direction of the field. If the magnetic field strength is 1.5 x 10-4T, what is the magnitude of the force acting on the particle?

F = 1.6 x10-16 N

Page 24: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Homework - Textbook

Pg.569 Force on a Wire: #7-9

Pg. 574 Force on a Moving Particle: #10-11

Page 25: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Defining Magnetic Field

Magnetic field hasn’t been defined qualitatively

Magnetic field is a force per unit current element

Electromagnetism is needed

Page 26: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Solenoid Picture

A solenoid is our first electromagnet Magnet caused by electricity

Page 27: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Solenoids

A solenoid is a coiled wire Contains many loops

Magnetic field of each loop sums to make the magnetic field of the solenoid http://webphysics.davidson.edu/Applets/BField/sol

enoid.html Capable of producing strong magnetic fields

Right Hand Rule 3: Coil fingers with the direction of current Thumb points in the direction of magnetic north

Magnetic field created is similar to a bar magnet

Page 28: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Right Hand Rule 3: SolenoidsRight Hand Rule 3:

Coil fingers with the direction of current Thumb points in the direction of

magnetic north

Page 29: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Diagram of a Solenoid’s Field

Where are the North and South Poles?

Page 30: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Homework

Calculating Magnetic Forces Exercises Handout

Page 31: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Lab Experiment

Lab Manual 24.1

Page 32: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Electric and Magnetic Fields

Page 33: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Research an Electromagnet

Pick from one among the list.Research about how it worksSpecifically, where is

electromagnetism involved and how does it make the device function?

2 minute presentation at the end of class explaining the device to the class

Include multi-media if possible!Questions?

Page 34: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

The List

SpeakersCathode Ray Tubes/TelevisionAlarmsElectromagnets for Lifting SteelGeneratorsElectric motorsMaglev trains

Page 35: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Technologies/Electromagnets Primitive motor

Make the Motor Generator

Reverse motor Electromagnet

How do you think this works? Speakers

http://electronics.howstuffworks.com/speaker5.htm

Cathode Ray Tube Alarm/bell Maglev trains

http://player.discoveryeducation.com/index.cfm?guidAssetId=6581C80B-C521-4467-9A8A-E56533E3FC83&blnFromSearch=1&productcode=US

Page 36: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

Summary of Hand Rules

Right Hand Rule 1: Point thumb in the direction of the current Make a fist Fingers show direction of magnetic field

Right Hand Rule 2: Make an L shape with your hand Thumb points in the direction of the current Fingers point in the direction of the magnetic field Palm shows the direction of the force

Right Hand Rule 3 (Solenoids): Coil fingers with the direction of current Thumb points in the direction of the magnetic field

Page 37: Physics 30S.  A changing magnetic field creates an electric field  A changing electric field creates a magnetic field  Basis for electricity generation,

The Plan!

Day 1 -2: What is Electromagnetism, Maxwell, Oersted, Field around a wire, Up to slide 16

Day 2: Force around a wire, Force on moving particles Up to slide 24

Day 3: Definition of Magnetism, Solenoids, In-class work Up to slide 26 Solenoid example

Day 4: Lab Experiment Day 5: Electromagnet applications research, summary of right

hand rules (Friday) – Gr. 11 up to here Up to Slide 36

Day 6: Review Day 7 Test