Physics 30S

 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

 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 Maxwell June 13,1831 – November 5, 1879

 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

 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

 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)

 Point your thumb in the direction of current flow  Fingers wrap to show direction of the magnetic field

 Point your thumb with the current  Curl your fingers to determine the direction of the field

 Permeability of free space  4π x Tm/A  Physical constant  Permeability relates the ability of the medium to induce a magnetic field  Inductance

 Current  Coming out of the screen  Going into the screen  Meant to visualize an arrow

Add arrows to show the direction of the magnetic field

a) What is the strength of the magnetic field 15 cm away from a wire carrying 75 A? B = 1.0 x T b) At what distance is the strength of the magnetic field 1.5 x T? r = 1.0 m

a) How much current is a wire carrying if the magnetic field is measured to be 3.03 x T at 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

 3. Magnetic Fields Homework Handout

 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)

What direction is the force on the wire? Solution: Into the screen

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? F B = 0.08 N

What length of conductor, running at right angles to a T magnetic field and carrying a current of 20.0 A, will experience a force of 0.10N? I = 0.15 m

 Magnetic fields exert a force on moving electrical charges, including charged particles  What might the formula be?

 An electron is shot through a cathode ray tube TV at 5.0 x 10 5 m/s, perpendicular to the direction of the field. If the force acting on the particle is 2.0 x N and the length of the tube is 10 cm, what is the strength of the magnetic field?  B = T

 An alpha particle (He 2+ ) is shot through a magnetic field at 3.33 x 10 6 m/s, perpendicular to the direction of the field. If the magnetic field strength is 1.5 x T, what is the magnitude of the force acting on the particle?  F = 1.6 x N

 Pg.569  Force on a Wire: #7-9  Pg. 574  Force on a Moving Particle: #10-11

 Magnetic field hasn’t been defined qualitatively  Magnetic field is a force per unit current element  Electromagnetism is needed

 A solenoid is our first electromagnet  Magnet caused by electricity

 A solenoid is a coiled wire  Contains many loops  Magnetic field of each loop sums to make the magnetic field of the solenoid  oid.html oid.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:  Coil fingers with the direction of current  Thumb points in the direction of magnetic north

Where are the North and South Poles?

 Calculating Magnetic Forces Exercises Handout

 Lab Manual 24.1

 Pick from one among the list.  Research about how it works  Specifically, 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?

 Speakers  Cathode Ray Tubes/Television  Alarms  Electromagnets for Lifting Steel  Generators  Electric motors  Maglev trains

 Primitive motor  Make the Motor  Generator  Reverse motor  Electromagnet  How do you think this works?  Speakers   Cathode Ray Tube  Alarm/bell  Maglev trains  581C80B-C A8A- E56533E3FC83&blnFromSearch=1&productcode=US 581C80B-C A8A- E56533E3FC83&blnFromSearch=1&productcode=US

 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

 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