Chapter 18 Section 2

Identify the relationship between an electric current and a magnetic field

Compare solenoids and electromagnets

Describe how electromagnetism is involved in the operation of doorbells, electric motors, and galvanometers

Hans Christian Oersted – discovered the relationship between electricity and magnetism (1820)

Passing a compass under a wire carrying electric current

A compass moves its North-South orientation only when it is in a magnetic field different from Earth’s

Oersted concluded that an electric current produces a magnetic field

The direction of the field depends on the direction of the current

This marked the 1st research about electromagnetism

The magnetic field generated by the current is not very strong

2 devices can strengthen this magnetic field: Solenoid

Electromagnet

Suppose you made many loops in a wire carrying current?

The magnetic fields of the individual loops in a coil combine to make a stronger field (a solenoid)

Similar field as a bar magnet

http://www.societyofrobots.com/images/actuators_solonoid_magnetic_field.gif

A solenoid wrapped around an iron core

Makes the domains inside the iron core line up

100’s of times stronger than just a solenoid

Maglev trains (levitating trains)

http://georgeprice.net/wp-content/uploads/2009/11/electromagnet1.gif

http://www.pause-for-thought.co.uk/www/images/maglev.jpeg

Used in every day life…

Can be used to lift heavy objects containing iron

There are electromagnets in motors

2 solenoids in the doorbell make the doorbell work

Pushing the bell opens the circuit of the 1st solenoid; the current stops causing the magnetic field to drop and the light to go out; the change in the field causes the current in the second solenoid; this current induces a magnetic field that pushes an iron rod that sounds the bell

If a current-carrying wire can cause a magnet to move, can a magnet cause a current-carrying wire to move??

http://www.skoool.co.za/studynotes/science/uploadedImages/Coord12.20_motor_effect.gif

A device that converts electrical energy into mechanical energy

Armature: a loop or coil of wire that can rotate; located between the poles of a permanent magnet

Use direct current

Commutator: attached to the armature; reverses the direction of electric current in a wire

http://ffden-2.phys.uaf.edu/211.fall2000.web.projects/Kristian%20Swearingen/dcmotor.gif

Measures current

Contains an electromagnet placed between the poles of a permanent magnet

The poles of the electromagnet are pushed away by the poles of the permanent magnet

Electromagnet is free to rotate and is attached to a pointer

http://images.hobbytron.com/GI-1309-20-lg.jpg

Explain Oersted’s 1820 discovery

Explain how an electromagnet works