electromagnetic induction
DESCRIPTION
Physics 30S. Electromagnetic Induction. Electromagnetism. 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. Maxwell’s Equations. - PowerPoint PPT PresentationTRANSCRIPT
Electromagnetic Induction
Physics 30S
Electromagnetism
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
Maxwell’s EquationsComplicated, 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
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
Hans Christian OerstedOersted 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
Field around a Current Carrying WireCurrent 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)
Right Hand Rule 1Point your thumb in
the direction of current flow
Fingers wrap to show direction of the magnetic field
Visualizing the Magnetic Field around a Wire
Point your thumb with the current
Curl your fingers to determine the direction of the field
What is ?
Permeability of free space4π x 10-7 Tm/APhysical constantPermeability relates the ability of the
medium to induce a magnetic field Inductance
Notation
Current Coming out of the screen
Going into the screen
Meant to visualize an arrow
Example1 Right Hand Rule 1Add arrows to show the direction of
the magnetic field
Solution
Example 1: Calculating Fielda) 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
Example 2: Calculating Fielda) 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
Homework
3. Magnetic Fields Homework Handout
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)
Example 1 Right Hand Rule 2What direction is the force on the
wire?
Solution: Into the screen
Example 1: Calculating ForceA 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
Example 2: Calculating ForceWhat 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
What about Charged Particles? Magnetic fields exert a force on moving
electrical charges, including charged particles What might the formula be?
Example 1: Moving ParticlesAn 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
Example 2: Moving ParticlesAn 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
Homework - Textbook
Pg.569 Force on a Wire: #7-9
Pg. 574 Force on a Moving Particle: #10-11
Defining Magnetic Field
Magnetic field hasn’t been defined qualitatively
Magnetic field is a force per unit current element
Electromagnetism is needed
Solenoid Picture
A solenoid is our first electromagnet Magnet caused by electricity
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/sole
noid.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
Right Hand Rule 3: SolenoidsRight Hand Rule 3:
Coil fingers with the direction of current Thumb points in the direction of
magnetic north
Diagram of a Solenoid’s Field
Where are the North and South Poles?
Homework
Calculating Magnetic Forces Exercises Handout
Lab Experiment
Lab Manual 24.1
Electric and Magnetic Fields
Research an ElectromagnetPick 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?
The List
SpeakersCathode Ray Tubes/TelevisionAlarmsElectromagnets for Lifting SteelGeneratorsElectric motorsMaglev trains
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
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
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