Electric Current

1
Electric Current

• Chapter 21-3

2
Circuit

• A closed path through which electrons can flow
• Electrons flow because of a difference in
  potential
• When a switch is turned on it causes electron to
  flow

3
Flowing Electrons

• Remember that static electricity is the build up
  of electrons
• When the static charge causes a spark the flow of
  electrons that is created is very short
• Not long enough to run a light or a computer

4

• The electrons always flow from where there are
  more electrons (higher potential) to fewer
  electrons (lower potential)
• Static discharge quickly balances out the
  electrons and there is no more difference in
  potential

5
Current, I

• The flow of electrons
• The amount of current depends upon the number of
  electrons passing every second
• Measured in Amperes, Amps, A
• Measured with an ammeter

6
Ampere

• One ampere is one coulomb of charge passing every
  second
• One coulomb is 6.24 billion billion electrons

7
Potential Difference

• The difference in potential (the energy of the
  electrons) between two different places
• Measured in volts (V)
• Sometimes called voltage
• Measured with a voltmeter
• Doesnt depend upon the number of electrons only
  the energy the electrons carry

8
Batteries

• Current must maintain a difference in potential
  or the current will stop
• Batteries is a device that maintains that
  difference in potential

9
Resistance, R

• The opposition to the flow of electrons
• Measured in Ohms, W
• Copper is an excellent conductor because it has
  low resistance

10
4 Factors That Determine Resistance

• Length of the wire
• Thickness of the wire
• The type of material
• Temperature

11
Good Bad Resistance

• Toasters, hair dryers, Christmas lights
• Wiring

12
Ohms Law

• Determines a relationship between voltage,
  current and resistance

13

• If the resistance increases the current decreases
• A greater voltage in a circuit causes the current
  to increase

14
George Simon Ohm

• German physicist found experimentally

15

• The current in a metal conductor is directly
  proportional to the potential difference across
  it and inversely proportional to the resistance,
  Ohms Law
• V IR