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 AC We 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 Meter From a transformer, three wires go into our homes. Two are live and insulated carrying the alternating current The 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 Problem A 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 kW Time= 10 min= 0.166h x 5 days= 0.833h Energy used= Power x time = 1.2kW x 0.83h = 1.0 kWh Rate = $0.088/kWh Cost = energy use x rate = 1.0 kWh X $0.088/kWh = $0.088

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Phantom Loads The electricity that is used by an appliance when it is turned off. A stand-by mode Something that is turned on by a remote Clock 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

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