Electricity and Magnetism

CRCT review

just like gravityA force that depends on:

• Size (mass or charge of objects)

• Distance between the centers

What particle?• carries positive charge in the

atom? Where is it?• carries negative charge in

the atom? Where is it?• has no charge in the atom?

Where is it?

static electricity• Electric charges are

separated. More of either protons or electrons in one place.

• How? Move electrons

Ways to move electrons• friction – rub them from one

object to another• conduction – electrons flow

from touching objects• induction – electrons move in

response to electric field without objects touching

Electric current• What is electric current?

• What does an electric current cause?

• What is caused when the current is changing?

magnets• Electrons with same spin line

up and create magnetic domains.

• Permanent magnets: lots of aligned domains

• Cobalt, nickel and iron make good permanent magnets.

magnetic properties• Always has both north and

south pole

• Cut in half = two whole magnets

Earth’s magnetic poles

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/imgmag/mearthbar.gif

solenoid• Coil of wire

electromagnet• solenoid wrapped around an iron core

• The magnetic field inside iron magnifies the solenoid’s field

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/imgmag/sol3.gif

Stronger electromagnet

• More loops

• More current

Works other way too!• Move the magnet to get an

electric current. (Section 3)

http://media.web.britannica.com/eb-media/73/63373-004-CDB7E548.gif

Electric motor• An alternating current

causes a magnet to spin

• The magnet is attached to some mechanical device that spins (ex: fan blade)

Electric generator• A spinning magnet causes

an alternating current.

Circuits• energy source

• load

• wires

Circuitsseries

• lined up like train cars

• one current path

• same current everywhere

parallel

• branches

• more than one current path

• same voltage on each branch

Schematic of a DC circuit with three resistor in series

http://www.school-for-champions.com/science/dc_circuits.htm

Schematic of a DC circuit with three resistor in parallel

http://www.school-for-champions.com/science/dc_circuits.htm

V = IR• What happens to current if

voltage increases?

• What happens to current if resistance increases?

SI units• electric potential (aka: voltage)

= volt (V)

• current = ampere (A)

• resistance = ohm (Ω)

Decrease resistance in a wire

• shorter wire

• thicker wire

• cool the wire