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.

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 = or I = q/tCharge

time

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

Voltage Source

A battery or electrical outlet is a source of electric potential or voltage -charge.

The electrons that move in a conductor

arethe voltage source.

The net charge on a current-carrying

conductor is

Electromotive Force

An old-fashioned term for electric

potential or voltage is “

Electrical Resistance

Most materials offer some resistance to

the flow of electric charges through

them. This is called

.

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

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

Ohms’ Law

In symbols:

V = IRV

I R

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.

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.

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.

Converting AC to DC

AC is converted to DC using devices

called which allow charges to

move in only 1 direction.

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.

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