POTENTIAL DIFFERENCE AND RESISTANCE

POTENTIAL DIFFERENCE

The potential difference between two points in an electric circuit is the work done when a coulomb of charge passes between the points.
You can calculate the size of a potential difference using this equation:

Potential difference = Energy transferred or Work-done / charge

V = W / Q

V = W / Q

·         V is the potential difference in volts, V

·         W is the work done (energy transferred) in joules, J

·         Q is the charge in coulombs, C

THE VOLTS

The unit of potential difference is Volt (V). It is defined as energy consumption of one joule per electric charge of one coulomb.

1V = 1J/C

EXAMPLE:

A simple circuit has a p.d. of 11 V across it. Calculate how much electrical energy is transferred when a charge of 320C pass through it.

ANSWER

V =   W/ Q

W = VQ

= 11 V × 320 C = 3520 J

ELECTROMOTIVE FORCE AND POTENTIAL DIFFERENCE

Electromotive Force (e.m.f.) of a source is the energy converted from non-electrical to electrical form when one coulomb of positive charge passes through the source. The SI unit is Volt (V).

Potential difference between two points is defined as the energy converted from electrical to other forms when a coulomb of positive charge passes between the two points. The SI unit is Volt (V)

RESISTANCE

Resistance R is the opposition to the flow of current in electric circuits. It is the ratio of potential difference V across the conductor to the current I in it. Resistance is measured in ohms (Ω)

  R = V/I

THE OHM

The ohm can be defined as 1 volt per ampere       

OHM'S LAW

Ohm’s law states that: the current in a metallic conductor s directly proportional to the p.d. across its ends if the temperature and other conditions are constant.

EXAMPLE:

What is the resistance of a wire if a p.d. of 6.0 V drives a current of 0.25 A through it?

                                      R = V/I = 6.0 V/0.25 A =  24 Ω