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21.2 Electromagnetism In 1820 Hans Oersted discovered how magnetism and electricity are connected ______________. A unit of measure of magnetic field strength, the oersted _____________, is named after him. 21.2 Electromagnetism Electricity and Magnetism How can an electric charge create a magnetic field? How is an electromagnet controlled? How do galvanometers, electric motors, and loud speakers work? 21.2 Electromagnetism Electricity and Magnetism Electricity and magnetism are different aspects of electromagnetic a single force known as the ________________ force ____________. charged • The electric force results from ___________ particles. • The magnetic force usually results from the _______________ of _______________ motion electrons • in an atom. 21.2 Electromagnetism Electricity and Magnetism Magnetic Fields Around Moving Charges Oersted discovered an important physics principle… moving charges create a magnetic field vibrating • Moving charges may be the _______________ charges that produce an electromagnetic wave or the moving charges in a ______________. wire circles • Magnetic field lines form _____________ around a straight wire carrying a current. 21.2 Electromagnetism Electricity and Magnetism right If you point the thumb of your _________ hand in the direction of the current, your fingers _________ curl in the direction of the magnetic field. Direction of current Direction of electron flow Current-carrying wire Direction of magnetic field 21.2 Electromagnetism Electricity and Magnetism Forces Acting on Moving Charges A magnetic field exerts a force on a moving charge. A charge moving in a magnetic field is deflected in a direction perpendicular to both the ________________ field and to the velocity of the charge. Force deflecting the charge Velocity of charge 21.2 Electromagnetism Electricity and Magnetism Forces Acting on Moving Charges A magnetic field exerts a force on a moving charge. A current-carrying wire in a magnetic field perpendicular will be pushed in a direction _____________ to both the field and the direction of the current. 21.2 Electromagnetism Electricity and Magnetism • Reversing the direction of the current will still cause the wire to be deflected, but in the opposite _______________ direction. • If the current is parallel ______________ to the magnetic field, the force no is zero and there is ____ deflection. 21.2 Electromagnetism Solenoids and Electromagnets loop If a current-carrying wire has a ________ in it, the magnetic field in the center of the loop points right through to left ____________ the loop. 21.2 Electromagnetism Solenoids and Electromagnets coil Multiple loops in the wire make a __________. combine The magnetic fields of the loops ___________ so that the coiled wire acts like a ______ bar magnet. 21.2 Electromagnetism Solenoids and Electromagnets The field through the center of the coil is the sum _______ of the fields from all the turns of the wire. A coil of currentcarrying wire that produces a magnetic field is called a solenoid ______________ 21.2 Electromagnetism Solenoids and Electromagnets ferromagnetic If a ________________ material, such as an iron rod is placed inside the coil of a solenoid, the increases strength of the magnetic field ______________. • The magnetic field produced by the current causes the iron rod to become a ____________. magnet electromagnet is a • An ________________ solenoid with a ferromagnetic core. • The current can be used to turn the magnetic field ____ on and ____. off 21.2 Electromagnetism Solenoids and Electromagnets The strength of an electromagnet depends on… current • the ___________ in the solenoid • the number of _________ in the coil loops • the type of _________ core The strength of an electromagnet can be ______________ using the following methods… increased • Increase the current flowing through the solenoid. • Increase the number of turns. easily • Use cores that are _____________ magnetized. 21.2 Electromagnetism Electromagnetic Devices Electromagnets can convert electrical energy into motion work ___________ that can do __________. • Common example: ______________ doorbells Electromagnetic devices such as galvanometers, electric motors, and electrical loudspeakers change ________________ energy into ______________ energy. mechanical 21.2 Electromagnetism Electromagnetic Devices Galvanometers A galvanometer is a device that uses a solenoid to _____________ small amounts of current. measure spring • A solenoid is attached to a ___________ and is free to rotate about an iron core. • The solenoid is placed between the ________ poles of two permanent magnets. • The greater the current, the more rotates the solenoid _____________. 21.2 Electromagnetism Electromagnetic Devices A galvanometer uses an electromagnet to move a _____________. pointer One common application is in an automobile gas gauge _______ _____________. The wire is connected to a ____________ in the gas tank. sensor 21.2 Electromagnetism Electromagnetic Devices Electric Motors An electric motor is a device that uses an electromagnet to turn an ____________. axle In this motor, a battery supplies current to a loop of wire through the _______________. commutator 21.2 Electromagnetism Electromagnetic Devices • When current flows through a loop of wire, the field of pushes the permanent magnet ___________ one side of the pulled loop. The other side of the loop is ____________. These forces rotate the loop. 21.2 Electromagnetism Electromagnetic Devices Loudspeakers solenoid A loudspeaker contains a _____________ placed pole around one _________ of a permanent magnet. The current in the wires entering the loudspeaker changes direction and increases or decreases. 21.2 Electromagnetism Electromagnetic Devices The magnetic force exerted by the permanent magnet moves the coil back and forth. As the coil moves, it causes a vibrate thin membrane to __________, waves that producing sound ________ match the original sound. Electrical energy converts to mechanical energy 21.2 Electromagnetism Assessment Questions 1. A charged particle is moving across a plane from left to right as it enters a magnetic field that runs from top to bottom. How will the motion of the particle be changed as it enters the magnetic field? a. b. c. d. It will accelerate. It will deflect either up or down on the plane. It will deflect perpendicular to the plane. Its motion will not be affected. Force deflecting the charge 21.2 Electromagnetism Assessment Questions 2. Which change will increase the strength of an electromagnet made by wrapping a conductive wire around an iron nail? a. b. c. d. reversing the direction of current flow replacing the nail with a wooden dowel increasing the number of coils of wire around the nail using a longer nail 21.2 Electromagnetism Assessment Questions 3. A loudspeaker uses a magnet to cause which energy conversion? a. b. c. d. mechanical energy to magnetic energy electrical energy to mechanical energy electrical energy to magnetic energy mechanical energy to electrical energy 21.2 Electromagnetism Assessment Questions 4. The motion of an electric charge creates an electrical field. True False Direction of current Direction of electron flow Direction of magnetic field