R Ch 34 Electric Current pg 1 Text Qs pg 545 RQ 1, 3-19,21,22

R Ch 34 Electric Current pg 1

Text Qs pg 545

RQ 1, 3-19,21 ,22

R 34.1 Flow of Charge pg 2

• Charges flow in a conductor when there is a difference in voltage (another name for voltage is potential). The flow will continue until both locations have the same voltage

R 34.2 Electric Current pg 3

• Electric current is the flow of electric charge.

• Solids only electrons flow• Liquids electrons & positive ions flow• Gasses electrons & positive ions flow• The overall or net charge of a conductor is

zero, as a new charge enters another charge leaves

R 34.3 Voltage Sources pg 4

• Cells are what we call batteries. Cells convert chemical energy to electrical energy

• Dry cell = flashlight battery• Wet cell = car battery• Two cells hooked together = battery• Generators like the alternator in your car &

power plant convert mechanical energy to electrical energy

R 34.3 Voltage Sources pg 5

• The electrons have potential energy leaving the negative terminal heading to the positive terminal.

• The electrons feel pressure to move. This pressure is called the voltage or EMF (electromotive force)

R 34.3 Voltage Sources pg 6

• At home the power company provides a 120 volts of potential difference or pressure between the two holes in the socket.

• This means there is 120 Joules of energy given to each Coulomb of charge (6 e18 electrons)

R 34.3 Voltage Sources pg 7

R 34.4 Electrical Resistance pg 8

• Electrical Resistance is a measure of how difficult it is for the electrons to flow through a wire & depends on;

• 1) material type, different metal has diff. resistanc

• 2) wire thickness, thicker wire = less resistance

• 3) length of wire, longer wire = more resistance • 4) temperature, higher temp = more resistance

R 34.5 Ohm’s Law pg 9

• Ohm’s law is the V = I x R

R 34.5 Ohm’s Law & Electric Shock pg 10

• Skin, shoes & clothes all provide a good deal of resistance to current electricity. Dry skin has about 500,000 ohms of resistance.

• If current travel through your body two things can happen;

• 1) overheating (cooking) tissue• 2) disrupt nerve function, stopping the heart

& or breathing

R 34.6 Ohm’s Law & Electric Shock pg 11

• To help someone who is being electrocuted;• 1) think• 2) use an insulator (probably wood or plastic) to break

contact between the body and the wire

• Birds contact wires all the time but do not get shock because;

• 1) their scaly feet are good insulators• 2) both feet are on the same wire, there is no

difference in voltage so no current flows from one foot to the other

R 34.7 Direct Current & Alternating Current pg 12

• Direct Current or DC current the charges only flow in one direction.

• Alternating Current or AC the charges vibrate back & forth and never move out of the wire

R 34.7 Direct Current & Alternating Current pg 13

• In North America the electron vibrates back and forth 60 times each second (due a change in voltage polarity) with a 120 volts of EPE

• Europe uses a 220 volt system because it is more efficient.

R 34.7 Direct Current & Alternating Current pg 14

• The 60 vibrations a second is called 60 cycle or 60 Hertz electricity.

• It means that for 1 / 120th of a second the wire is positive and for the next 1 / 120th of a second the wire is negative.

R 34.7 Direct Current & Alternating Current pg 15

• At your house there is a circuit breaker box call the electric service drop.

• A 120 volt negative wire and a 120 volt positive wire enter your house from the neighborhood electric line.

• Normally these are kept separate but they can be combined to make 240 volts for the air conditioning etc.

R 34.8 Converting AC to DC pg 16

• To convert the AC current that comes out of the wall socket to DC needed to run household devices requires three things;

• 1) a transformer, to lower or raise the voltage

• 2) a diode a one-way valve to eliminate the vibration back and forth

• 3) a capacitor to fill in the missing electrons

R 34.8 Converting AC to DC pg 17

R 34.9 The Speed of Electrons in a Circuit pg 18

• DC current electrons moves about 0.01 cm/sec because the electrons keep bouncing off the positive nucleus which are in the way.

• AC current electrons just vibrate back and forth and don’t go anywhere

• An electric field is what really moves through the wire at close to the speed of light

R 34.10 The Source of electrons in a Circuit pg 19

• So the truth is electrons do not come out of a wire into a light bulb. An electric field comes out of the wire and pushes and or pulls on the electrons in light bulb.

• The electric field caused the electrons to move and do work. Just like a magnet would push or pull a metal ball bearing.

R 34.10 The Source of electrons in a Circuit pg 20

• When you get an electric “shock” what you feel is the electrons in your body being pushed & pulled 60 times each second with 120 Joules of EPE.

R 34.11 The Source of electrons in a Circuit pg 21

• Electric power is the rate at which electric energy is converted to heat, light or mechanical energy.

• The electric company sells you Kilowatt-hours of energy, (not Joules of energy)

• So 10 100 watt light bulbs burning for one hour is 1 kw-hr of electric energy.