This document discusses key concepts in electricity including potential difference, current, voltage, resistance, Ohm's Law, direct current, alternating current, and electric power. It defines potential difference as the loss of potential energy for charges moving from high to low voltage locations. Current is defined as the flow of electric charge past a point over time. Ohm's Law states that current is directly proportional to voltage and inversely proportional to resistance in many conductors. Direct current maintains voltage polarity while alternating current switches polarity periodically.

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