Lesson V “Electromagnetism”
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Transcript of Lesson V “Electromagnetism”
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Lesson V “Electromagnetism”
Matter & Energy
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S.W.B.A.T.
• Explain how an electric charge creates a magnetic field
• Describe how electromagnets are used
• Relate electromagnets to everyday devices
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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
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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
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Electricity & Magnetism
• Flowing electric charges create magnetic fields
• Magnetic field lines form circles or loops around a flowing charge moving through a straight wire
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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
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“Right-Hand Rule”
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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)
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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
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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
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Electromagnets• Increasing the current will increase
the electromagnet’s strength• Increasing the amount of wire loops
in the solenoid will also increase electromagnetic strength
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Electromagnetic Devices• Electromagnetic devices include
electric motors, galvanometers, loudspeakers and generators
• Electric motors use electromagnets to turn an axle
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• 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
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How an Electric Motor Works
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• 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
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• 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
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• 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
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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
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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”
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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