Lesson V “Electromagnetism”

Matter & Energy

S.W.B.A.T.

• Explain how an electric charge creates a magnetic field

• Describe how electromagnets are used

• Relate electromagnets to everyday devices

Electricity & Magnetism

• Along with gravity and the strong & weak nuclear force, electromagnetism makes up one of the four known forces in the universe

• Electricity & magnetism are two parts of the same force

Electricity & Magnetism

• Hans Oersted (1820) discovered through experiments that electricity and magnetism were related

• Oersted showed that electric current moving through a wire deflected a compass needle

Electricity & Magnetism

• Flowing electric charges create magnetic fields

• Magnetic field lines form circles or loops around a flowing charge moving through a straight wire

Electricity & Magnetism

• Electric charges moving through a magnetic field will be shifted 90o from its direction of movement and from the magnetic field loop

• If the current flow is reversed the charges will shift 90o in the opposite direction

“Right-Hand Rule”

Electricity & Magnetism

• If the current is moving parallel with the magnetic field loop then there is no deflection

• Electric fields are different than magnetic fields in that it exerts a force on a charge in the same or opposite direction (+ or – charge)

Electromagnets

• Looping a wire into a coil will create a combined magnetic field

• A solenoid is created when a current is passed through the looped wire

Electromagnets

• An electromagnet is made when an iron core is placed inside the looped wire or solenoid

• Electromagnets are very strong magnets that can change strength & direction with a change in current

Electromagnets

• Increasing the current will increase the electromagnet’s strength

• Increasing the amount of wire loops in the solenoid will also increase electromagnetic strength

Video (3:18) “Electromagnetism: Magnetic Force”

Electromagnetic Devices

• Electromagnetic devices include electric motors, galvanometers, loudspeakers and generators

• Electric motors use electromagnets to turn an axle

• Electric motors contain a central iron core that is wrapped by many loops of wire (solenoid)

• As the current flows through the wires magnetic fields are created

• The magnetic fields create a push & pull which forces the axle to turn

Electromagnetic Devices

How an Electric Motor Works

• A galvanometer uses an electromagnet to measure small amounts of current

• Galvanometers are used to gauge how much gasoline is left in a car & for laser guidance systems

Electromagnetic Devices

• Loudspeakers use a solenoid wrapped around one pole of a permanent magnet

• Sound is reproduced as the changing current produces a change in magnetic fields

Electromagnetic Devices

• The magnetic force moves the solenoid back & forth causing a thin membrane to vibrate

• These vibrations produce sound waves from the speaker which closely matches the original sound

Electromagnetic Devices

Electromagnetic Devices

• Generators (AC & DC) convert mechanical energy to electrical energy

• A rotating coil of wire (or solenoid) placed in a magnetic field will generate an electric charge

Electromagnetic Devices

• The electric charges are induced into a wire which then creates an electric flow

• Generators resemble electric motors but generate electricity instead of using it (the opposite of electric motors!)

Video (3:49) “World’s First Electric Generator”

Class Activity

• List three devices (not mentioned in this lesson) that use electromagnetic forces

• Explain what each device does and how electricity & magnetism interact in the device