Ohm’s Law

And the basics of CIRCUITS

The Concept of Potential Difference POTENTIAL DIFFERENCE

- the work done or energy needed in moving a unit electric charge between two points in an electric field

Sources of Potential Difference1. electric cells – uses chemical energy2. generators – uses mechanical energy3. solar cells (or photovoltaic cells) – uses light energy

EMF vs.Voltage Electromotive Force (emf)

- the potential difference between the terminals of a cell when no current flows

Terminal Voltage (or simply voltage, V) or J/C- the potential difference between the terminals of a cell when current flows

  Since a cell has an internal resistance that

requires energy (or potential difference) to overcome, then the terminal voltage is always less than the electromotive force.

( V < emf )

Current and Resistance ELECTRIC CURRENT ( I )

- amount of charge passing through any point in a conductor per unit time I = Q / t unit: C/s or ampere (A); 1C/s = 1A

RESISTANCE ( R )- the opposition a material offers to the flow of charges

through it- the SI unit of resistance is ohm (Ω) or J.s / C2

- named after George Simon Ohm

OHM’s LAW it states that in an electric circuit;

the current (I) passing through a conductor varies directly as the potential difference (V) applied at its ends and inversely as the resistance (R) of the conductor; this maybe applied to the entire circuit or to a particular part of a circuit

OHM’s LAWOPERATIONAL DEFINITION

I = V / R

Units: I --- amperes (A); 1A = 1C/s

V – volt (V)

R – ohm (Ω)

Simple Circuits SERIES CIRCUIT a simple circuit that

contains more than one piece of electrical apparatus (or resistors) connected one after the other in a single line

in this circuit, the current flows in a single path and is the same in all parts; and the current stops flowing whenever a part of the circuit fails

Simple Circuits PARALLEL CIRCUIT a simple circuit where two

or more pieces of electrical apparatus (or resistors) are connected side by side so that the current is divided between them

in this circuit, each apparatus operates independently of the others so even if one piece fails, current still flows through the others