17. The circle containing E, I, and R is divided into two parts, with E

above the line and I and R below the line.

To determine an unknown

quantity, first cover that quantity with a finger.

The position of the

uncovered letters in the circle will indicate the mathematical operation to

be performed. For example, to find I, cover the I

FIGURE 6.

DETERMINING VOLTAGE IN A BASIC CIRCUIT.

with a finger.

The uncovered letters indicate that E is to be divided by R,

To find the formula for E, cover E with your finger. The result indicates

that I is to be multiplied by R, or E = IR.

To find the formula for R,

cover R. The result indicates the R is to be divided by I,

You are cautioned not to rely wholly on the use of this diagram when you

transpose the Ohm's law formulas. The diagram should be used to supplement

your knowledge of the algebraic method.

Algebra is a basic tool in the

solution of electrical problems.