2. Potential Difference
 Charges can “lose” potential energy by
moving from a location at high potential
(voltage) to a location at low potential.
 Charges will continue to move as long
as the potential difference (voltage) is
maintained.

3. Current
 A sustained flow of electric charge past
a point is called an
Specifically, electric current is the rate
that electric charge passes a point, so
Current = C h a r g e or I = q/t
time

4. Measuring Current
 If 1 Coulomb of charge (6.25 x 1018
electrons) passes a point each second,
the current is
 So, 1 Ampere = 1 Coulomb/sec

5. Voltage Source
 A battery or electrical outlet is a source
of electric potential or voltage -
charge.
The electrons that move in a conductor
are
the voltage source.
The net charge on a current-carrying
conductor is

6. Electromotive Force
 An old-fashioned term for electric
potential or voltage is “

7. Electrical Resistance
Most materials offer some resistance to
the flow of electric charges through
them. This is called
.

8. Resistance
Resistance of a conductor depends on:
- Gold is best
- longer conductors have more
resistance.
- thick wires have less
resistance than thin wires
- higher temperature means
more resistance for most conductors

9. Ohm’s Law
For many conductors, current depends
on:
 Voltage - more voltage, more current
 Current is proportional to voltage
 Resistance - more resistance, less
current
 Current is inversely proportional to
resistance

10. Ohms’ Law
 In symbols:
V = IR
V
I R

11. Direct Current
 If the voltage is maintained between
two points in a circuit,
- from high to low
potential. This is called
 Battery-powered circuits are dc circuits.

12. Alternating Current
 If the high & low voltage terminals
switch locations periodically, the
in
the circuit. This is called
 Circuits powered by electrical outlets
are AC circuits.

13. AC in the US
 In the US, current changes direction
120 times per second, for a frequency
of 60 cycles per second or 60 Hertz.
Normal outlet voltage in the US is 110-
120 volts, although some large
household appliances run on 220-240
volts.

14. Converting AC to DC
 AC is converted to DC using devices
called which allow charges to
move in only 1 direction.

15. Speed of Electrons
 Electrons in a circuit do move
quickly - they actually “drift” at about 1
mm/s.
 It is the
- at about the speed of light -
through the circuit and carries the
energy.

16. Electric Power
Power = energy/time = current x voltage
 P = IV = I2R
 1 Watt = (1 Amp)(1 Volt)
 1 kilowatt = 1000 Watts
 A kilowatt-hour is a unit of energy