ELECTROMAGNETISMMagnetism from Electric Currents

CHAPTER 18, Section 2, pages 626-631

1820: Denmark

Hans Christian Oersted

?

I. The DiscoveryA. In the year _____, the Danish physicist

____________________ observed that:

A compass needle (placed near a wire) moves as soon as current flows through the wire

B. When Oersted reversed the current direction in the conductor the compass needle…

moved in the opposite direction

1820Hans Christian Oersted

1. A current flowing through a conductor produces a magnetic field

C.From these observations, Oersted concluded that:

2. The direction of this magnetic field depends on the direction of the current

A. The magnetic field around a current-carrying wire forms a _________ around the conductor.CIRCLE

II. ELECTROMAGNETISM

B. The __________________ is used to find the direction of the ________________ produced by a current

•THUMB - points in the direction of the ___________

•FINGERTIPS - point in the direction of the _______________

RIGHT-HAND RULEMAGNETIC FIELD

CURRENT

MAGNETIC FIELD

C. Solenoids• a __________ is a _____ of wire with an electric current in it.

• it acts as a _________ when current passes through it (has a ________________)

SOLENOID COIL

MAGNETMAGNETIC FIELD

•The _______________ of each loop ______ to the strength of the magnetic field of any neighboring loops.

•If the current changes direction, the ________________ changes direction and the _______ flip (use a __________ to test)

MAGNETIC FIELD

COMPASS

MAGNETIC FIELD

POLES

ADDS

• To INCREASE a solenoid’s magnetic field:

1. ___________________________________

2. __________________________________

*3. __________________________________Place ferromagnetic material in center of coils

* This makes an ___________________. ELECTROMAGNET

Increase the # of coils (combines magnetic fields)

Increase the voltage (which increases current)

D. ELECTROMAGNETS• Much ___________ than solenoids themselves because the magnetic field of the ______ causes the ferromagnetic core to become a ________. The _________ of the core line up and create a larger magnetic field.

Ex: “magnet charger”

STRONGERCOILS

MAGNETDOMAINS

• Electromagnets may be turned ______ depending on if ________ is flowing.

ON/OFFCURRENT

III. ELECTROMAGNETIC DEVICESA. Galvanometer/Ammeter –

• Have an _________________ (attached to a pivoting needle) that interacts with a ____________ magnet to measure __________

ELECTROMAGNET

PERMANENT

CURRENT

CURRENT

•The stronger the __________ through the coils, the greater the attraction/repulsion with the permanent magnet.

CURRENT

B. Electric Motor• converts (changes) ____________ energy into _____________ energy (motion)

ELECTRICALMECHANICAL

Motors in your house use AC

DC MOTOR

1. e- flow from the battery, through the _______ to the ___________ and then through the ____ of an electromagnet.

commutatorbrushescoils

Brushes

Permanent magnet

Coil

Commutator

ArmatureElectrons always flow in the same direction: from negative to positive.

2. Magnetic field of the ____________ magnet interacts with the magnetic field of the _________________ (opposites _________, like poles ______)

3. The brushes lose contact with the “split-ring” ______________. Current is turned off, but the __________ still spins due to ________.

PERMANENT

ELECTROMAGNETATTRACT REPEL

COMMUTATOR

ARMATURE

INERTIA

4. The brushes touch the _____________ again and current flows through the coils in the __________ direction. The poles ________ and the coil repels and spins!

COMMUTATOR

OPPOSITESWITCH

5. This process continues. As current changes direction the _______________ changes direction.

MAGNETIC FIELD

Attract…repel….attract…repel….attract…repel….

the electric motor spins!