Page 335 - NS-2 Textbook

330 NAUTICAL SCIENCES

I = current in amperes
E = voltage in volts
R = resistance in ohms
If any two of the quantities in the equation are known,
the third may be easily found.

E R Example: Circuit 1 contains a resistance of 1.5 ohms
and a source voltage of 1.5 volts. How much current
flows in the circuit?
Soilltion: I = E/R = 1.5 V /1.5 n = 1 ampere
In many circuit applications, the current is known, and
either the voltage or the resistance will be the unknown
quantity. To solve a problem in which current and resis-
tance are known, the basic formula for Ohm's law must
be transformed to solve for E. Multiplying both sides of
Schematic diagram of a basic circuit. A battery is designated by the the equation by R, the formuia for finding voltage is: E =
symbol E; a light bulb is the resistance, labeled R.
IR (Equation B).
Similarly, to h'ansform the basic formuia when resis-
tance is unknown, multiply both sides of the basic equa-
probably easier to understand, so that is the concept used
tion by R and then divide both sides of the equation by I.
herein for our discussion of electricity.
The resulting formula for resistance is: R = E/I (Equa-
A schematic is a diagram in which symbols are used
tion C).
for a circuit's components, instead of pictures. These
symbols are used in an effort to make the diagrams eas-
ier to draw and easier to understand. Schematic symbols
POWER
aid the technician who designs or repairs electrical or
electronic equipment. Electrical power refers to the rate at which work is being
done. Work is done whenever a force causes motion.
OHM'S LAW Therefore, since voltage makes current flow in a closed
circuit, work is being done. The rate at which this work
In the early 1800s, George Simon Ohm proved that a def- is done is called the electric power rate, and its measure is
inite relationship exists among current} voltage, and re- the watt-the basic unit of power. Power is equal to the
sistance. This relationship, called Ohm's law, is stated as voltage across a circuit, multiplied by the current
follows: The current in a circuit is directly proportional to
the applied voltage and inversely proportional to the cir-
cuit resistance. Ohm's laV\T may be expressed as an equa-
tion: I = E/R (Equation A).

E R

1.5v 1.5f1.

I= ? Summary of basic formulas for Ohm's law and for power. In each
quadrant of the circle are three formulas. Each formula can be used
to find the unknown factor whose symbol appears in the adjacent
Circuit 1. Determining current in a simple circuit. quadrant of the central circle.