Peoples Physics Book Version-2

http://www.ck12.org Chapter 14. Electric Circuits Version 2

14.2 Circuit Basics

We use the following symbols to represent the quantities discussed above:

TABLE14.1:Circuit Quantities

Name Symbol Electrical Symbol Units Everyday device

Voltage V Volts (V) Battery, the plugs in

your house, etc.

Current

(flow of

charge)

I=∆∆qt Amps (A)

A=C/s

Whatever you plug

into your wall sock-

ets draws current

Resistance R Ohm(Ω) Light bulb, Toaster,

etc.

Loop and Junction Rules for Voltage/Current

In electriccircuits(closed loops of wire with resistors and constant voltage sources) energy must be conserved. It

follows that changes in energy density, the algebraic sum of voltage drops and voltage sources, around any closed

loop will equal zero.

In an electricjunctionornodethere is more than one possible path for current to flow. For charge to be conserved at

a junction the current into the junction must equal the current out of the junction.

Ohm’s Law

The resistance of an object — described above — is quantified as the ratio of the voltage drop across it to the amount
of current that will flow from that voltage. Note that the current depends on the voltage drop; here, as above we use
Vinstead of∆Vto mean voltage difference (both are accepted ways).

R=

V

I

[1] Definition of Resistance

Generally, more current flowing through a resistor will cause a higher voltage drop. For the special class of resistors

discussed in this class this ratio is a constant — the current flowing across these resistors will rise at the same rate as

the voltage difference supplied. In other words, theresistance does not depend on the amount of current that flows

through the resistor, or the voltage drop across it. This relationship is known asOhm’s Law, for a constant current

it is usually written as

V=IR [2] Ohm’s Law