13.3 Alternating Current

Alternating Current• An electric current that periodically changes direction• Current induction in a coil reverses direction

periodically due to having to move the magnet back and forth to keep the magnetic field changing• Direct current studied in chapter 11 only works for

small circuits. • The transfer of electrical energy using direct current is

limited to how far it can be transferred without significant energy loss in the form of thermal energy• Thomas Edison built first power station and was only

able to deliver to 193 buildings

What is Alternating Current?

• Voltage and Current vs time• Frequency of 60Hz• Current reverses direction 60 times a second• Electrons are essentially in one spot• So fast, we can’t detect it with our eyes

Household Circuits

• Apartments and small homes require 50A - 100A of electric current• Larger homes 100A – 200A• Homes are designed to have 240V of service• Electric stoves and dryers are some of the

appliance that need this high of voltage. • Other appliances use 120V

Three wire system• Allows to accommodate both 240V and 120V appliances• Red and black = “live” wires or “hot” wires• The WhiteWhite =“neutral”• Voltage between red and black is 240V• Voltage between the red and whitewhite or black and whitewhite is

120V• Typically electricians use black and whitewhite for outlets the

require 120V and red and black for outlets that require 240V• Ground wire = green or bare = electrically connected to

the ground, preventing stray currents from reaching you, directing them to the ground

Receptacles• 240V service = 3 or 4 prong plugs (one for

each wire)• 120V service = 2 or 3 prongs (black, whitewhite

and green)• Small devices such as lamps may only have

two, not having the ground wire• Some devices such as lap tops require direct

current and have an adapter within their power cord

Common Household Appliances

Safety• When too much current flows through your circuits…• Fuses: wire in fuse melts and breaks the circuit. Must

replace the fuse• Circuit Breakers: Bimetallic strip heats up and bends

which “trips” the breaker and turns of the circuit. Reusable and can be reset• Ground Fault Circuit Interrupters (GFCI’s): used in

bathroom outlets. Detect difference in current going into the circuit (if you create a circuit by having a wet hand when plugging in an appliance)• Arc Fault Circuit Interrupters (AFCI’s): prevent sparks

or arcing if insulation around wire becomes frayed

Homework• Pg 598 #’s 1-6