Generating and Using Electricity

Direct Current and Alternating Current

The current from a cell is called direct current

The electrons only travel in one direction in DC

Alternating current (AC) is when the electrons move back and forth in a circuit.

AC is the type of current that is delivered to our homes and schools.

Advantages of ACWe can transmit extremely high voltage

electrical energy which saves on loss of energy as heat.

Our homes use a lot less potential difference than that which travels through transmission tower wires.

In order to use this energy, we need to change the size of potential difference of the alternating current using a transformer.

Transformers cannot work with direct current.

The MeterFrom a transformer, three wires go into our

homes. Two are live and insulated carrying the

alternating currentThe third is the ground which is neutral and not

insulated.The meter registers the amount of energy that

is used in your home.After passing through the meter, the electrical

supply is connected to a distribution panel.The panel consists of either circuit breakers or

fuses for safety.

Safety

Ground fault circuit interrupter has a small circuit breaker if there is any difference in current between the right and left slot. Used when near water.

Surge protector prevents damage to circuits in electronic devices during power surges caused by lightning.

Power Ratings

A factor that affects the amount of electricity used in your home is the power ratings of your appliances

Electrical Power is its rate of use of electricity and is measured in watts (W) or kilowatts (kW) which is 1000 watts

Amount of Use

Electrical energy that is used is calculated by multiplying the power rating of an appliance by the amount of time it is used for.

Measured in kilowatt hours (kWh)The cost of electrical energy

depends on the amount of energy used and the price per kWh.

Sample ProblemA hair dryer is rated at 1200W. It is used for 10

min each school day, when the cost of electrical energy is $0.088/kWh. What is the cost of using the hair dryer on all five school days during one week.Power = 1200W = 1.2 kWTime= 10 min= 0.166h x 5 days= 0.833hEnergy used= Power x time

= 1.2kW x 0.83h = 1.0 kWh

Rate = $0.088/kWhCost = energy use x rate

= 1.0 kWh X $0.088/kWh = $0.088

You Try it!

P. 495 #1-5

Phantom Loads

The electricity that is used by an appliance when it is turned off.

A stand-by modeSomething that is turned on by a

remoteClock displays on microwave,

coffee maker, etc.

Efficiency

The ratio of useful energy output to total energy input, expressed as a percentage.

Percent = useful energy output x 100% efficiency total energy input

You Try It!

P. 498 #1-4P. 500 #1,2,4-6,8,9.