Man's physical universe

xanabras

408 MAGNETISM AND ELECTRICITY

Ohm's law may now be stated as follows:

or

Current = -Y^ltage.

Resistance

Amperes = Volts

Ohms

or, using accepted abbreviations,

T

/p t\ = E (Electromotive force)

R (Resistance)

The electromotive force is

the maximum potential difference of a

cell, that is, the potential difference that exists when no current is

being drawn from the cell. The resistance in this formula refers to the

total resistance in a circuit, both internal and external.

Electrical Power Is Measured in Kilowatt-hours.

Electric power is paid for in terms of watt-hours rather than volts

or amperes. The watt is equal to the product of the voltage times the

number of amperes, just as

in proper units,

T7I

• 1

D v/ Volume

I'luid power = rressureX

Seconds

Volts X Amperes = Watts

The kilowatt-hour, the most common electrical-energy unit, is the

energy delivered in an hour at the constant rate of one kilowatt.

Everyone should be able to make simple calculations which will

enable him to determine the relative cost of operation of his various

electrical appliances. Supposing that electrical current costs five

cents per kilowatt-hour, what would it

appliances for one hour?

cost to operate the following

Appliance

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