household electrical energy

Household Electrical Energy

BC Science Probe 9Section 11.4


• Energy has always been used in homes for heating, cooking and lighting, but it was not always electrical energy.

• The first electric light was called an arc lamp. – It had two carbon electrodes that touched then

pulled apart slowly so that the current would arc between the electrodes.

– These were safer than gaslights, but difficult to use.


• In 1879 everything changed!• Thomas Edison revolutionized home lighting

with the incandescent light bulb.

The History of the Electrical Power Industry

• Since Thomas Edison had invented the incandescent light bulb, he needed ways to generate and transmit energy that the light bulb would need.

• In 1882 in New York, Edison opened the first electrical power plant which provided electricity to 59 customers.


• The system that he built used about 100V of direct current (DC).

• Remember that DC electricity only flows in one direction!


• Edison’s system had a couple of problems with it:– Low voltage (100V) so large currents were needed

to supply small amounts of power and really large copper wires were needed to carry it.

– The purpose was to sell the energy, but it was difficult to determine how much energy was consumed.


• George Westinghouse came along and figured out that the solution was using a higher voltage.

• Westinghouse recruited Nikola Tesla and they developed a commercially useable electrical transformer.


• A transformer is a device that can raise or lower voltages.– It requires alternating current (AC) where the

current flows back and forth.


• 1896 was when electrical energy started being produced using hydroelectric power. (It started in Buffalo, NY)– This first transmission line carried about 800 KW

of power.– As demand increased, lines were added.– Today, voltage is transmitted at hundreds of

thousands of volts, which allows large amounts of power to be sent using relatively low currents.

The Electric Meter

• Now that Westinghouse had developed the transformer and gained control of electrical distribution, he needed a way to accurately measure how much electrical energy a customer used.

• In 1894, the Westinghouse Company produced the first induction watt·hour meter to measure electrical energy consumption in watt·hours.

The Electric Meter

• Energy is usually measured in joules.

• Since ΔE = PΔt, or power (in watts or kilowatts) multiplied by time (in hours), the watt·hour can also be used as a unit of electrical energy.

The Electric Meter

• The meters we use today are often called kilowatt·hour meters because they measure the amount of electrical energy in kilowatt·hours (kW·h)

The Electric Meter

• An average BC home uses about 800 kW·h of electricity per month.

• The energy used will depend on things like the season, how the home is heated or cooled, how many people live in the home, etc.

The Electric Meter

• How much is 800 kW·h in joules?

• 800 kW·h × 1000 W/ 1 kW × 3600 s/ 1h =

2,880,000,000 J

The Electric Meter

• 2,880,000,000 J = 2.88 GJ (Gigajoules)

• This is a huge number which is why we use kW·h instead of joules to sell energy.

Determining Electrical Energy Costs

• The electric meters that we will look at in class use rotating pointers on dials and they alternate between clockwise and counterclockwise directions.


• Reading a meter from left to right, the dials represent ten thousands, thousands, hundreds, tens and ones in units of kW·h.

• Look at figure 4 on page 351. What is the reading on that meter?


• It is important to know that when the pointer is between two numbers, that you read the smaller one!


• Reading a meter from left to right, the dials represent ten thousands, thousands, hundreds, tens and ones in units of kW·h.

• Look at figure 4 on page 351. What is the reading on that meter?– 94,761 kW·h


• The meter does not get set to zero every time that it is read, so month to month, the electrical company calculates the difference between this reading and the last to determine how much electrical energy was used.

• Then the multiply that difference by the rate set by the company to figure out the electric bill.

EnerGuide Labels

• All household appliances are sold with an EnerGuide label which tells us about how much electrical energy the appliance will use.

• It tells us about how many kW·h it should use in a typical year.

• These ratings are updated every few years as appliances get more and more efficient.

Sample Problem 1

• Reading a kW·h meter and determining the cost of electricity– Determine the reading of the kW·h meter in

figure 5 on page 351.

Sample Problem 1

• Reading a kW·h meter and determining the cost of electricity– Determine the reading of the kW·h meter in

figure 5 on page 351.• 62,335 kW·h

Sample Problem 1

• Reading a kW·h meter and determining the cost of electricity– This meter reading was taken on the last day of

the month. The meter reading from last month was 61,409 kW·h. How much electrical energy was used this month?

Sample Problem 1

• Reading a kW·h meter and determining the cost of electricity– This meter reading was taken on the last day of

the month. The meter reading from last month was 61,409 kW·h. How much electrical energy was used this month? • Subtract last month’s reading from this month’s.• 62,335 kW·h - 61,409 kW·h = 926 kW·h

Sample Problem 1

• Reading a kW·h meter and determining the cost of electricity– If the electricity company charged $0.065/ kW·h,

how much did the electricity cost for the month?

Sample Problem 1

• Reading a kW·h meter and determining the cost of electricity– If the electricity company charged $0.065/ kW·h,

how much did the electricity cost for the month?• Multiply the amount of electrical energy used by the

rate ($0.065/ kW·h)• Cost = (926 kW·h) ($0.065/ kW·h) = $60.19

Assignment

• CYU p. 354• # 2-12

household electrical energy

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