R Ch 34 Electric Current pg 1

1
R Ch 34 Electric Current pg 1

• Text Qs pg 545
• RQ 1, 3-19,21 ,22

2
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

3
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

4
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

5
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)

6
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)

7
R 34.3 Voltage Sources pg 7
8
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

9
R 34.5 Ohms Law pg 9

• Ohms law is the V I x R

10
R 34.5 Ohms 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

11
R 34.6 Ohms 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

12
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

13
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.

14
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.

15
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.

16
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

17
R 34.8 Converting AC to DC pg 17
18
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 dont go anywhere
• An electric field is what really moves through
  the wire at close to the speed of light

19
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.

20
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.

21
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.