in the formula should be noted. The reason for this

is that future circuits may have several currents, and

it will be essential to differentiate between IT and

other currents.

To compute any quantity (E, I, R, or P) associated with a single given

resistor, the values used in the formula must be obtained from that

particular resistor.

For example, to find the value of an unknown

resistance, the voltage across and the current through that particular

resistor must be used.

To find the value of a resistor:

To find the voltage drop across a resistor:

ER = IR x R

d. *Kirchhoff's Voltage Law. * In 1847, G. R. Kirchhoff extended the use

of Ohm's law by developing a simple concept concerning the voltages

contained in a series circuit loop. Kirchhoff's law states: "The algebraic

sum of the voltage drops in any closed path in a circuit and the

electromotive forces in that path is equal to zero."

To state Kirchhoff's law another way, the voltage drops and voltage sources

in a circuit are equal at any given moment in time. If the voltage sources

are assumed to have one sign (positive or negative) at that instant and the

voltage drops are assumed to have the opposite sign, the result of adding

the voltage sources and voltage drops will be zero.

The terms electromotive force and EMF are used in

explaining Kirchhoff's law when used in alternating

current (ac) circuits. In applying Kirchhoff's law to

direct current (dc) circuits, the terms electromotive

force and EMF apply to voltage sources such as

batteries or power supplies.

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