Ohm's Law

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George Simon Ohm proved by experiment that there is a precise relationship between voltage, resistance, and current in a circuit. He published his findings, now known as ohm’s law, in 1826.

OHM’S LAW

Ohm’s law is stated as: I = E / R

Where I = current in amperes, E = electromotive force in volts, R = resistance in ohm’s

CURRENT CALCULATIONS

Current varies inversely with resistance. With a constant voltage, if resistance is increased the current flow decreases; if resistance is decreased the current flow increases.

VOLTAGE CALCULATIONS

Ohms law can be transposed to determine voltage when the resistance and current are known.

Ohm’s can also be stated as: E = IR

Where I = current in amperes, E = electromotive force in volts, R = resistance in ohm’s

RESISTANCE CALCULATIONS

Ohms law can be transposed to determine resistance when the voltage and current are known.

Ohm’s can also be stated as: R = E / I

Where I = current in amperes, E = electromotive force in volts, R = resistance in ohm’s

WORK AND ENERGY

Work is when a force acts to produce motion in a body.

Energy is the ability to do work.

W = QV

Where W = work or energy, Q = charge (C), V = potential difference (V)

POWER

Power is the rate at which work is done.

P = W / t

Where  P = power (W), W = work (J), T = time (s)

P = EI

Where  P = power in watts, E = electromotive force in volts, I = current in amperes

P = I² R

Where  P = power in watts, I = current in amperes, R = resistance in ohms

P = E² R

Where  P = power in watts, E = electromotive force in volts, R = resistance in ohms

POWER RATING

Many electrical components are given a power rating which indicates the rate at which the converts electrical energy to another form of energy. An example is a 100 watt light bulb which can convert more electrical energy into light energy in a given amount of time than a 60 watt light bulb (assuming both bulbs are used connected to a standard 120 volt supply).

Resisters are commonly rated for maximum power in watts. Any combination of voltage or current may be used as long as the wattage is not exceeded.

POWER CONVERSION AND EFFICIENCY

An electric motor converts electrical energy into mechanical energy. An electric light bulb converts electrical energy into light energy.

The ratio of power converted to useful energy divided by the power consumed by a device is its efficiency.

Efficiency = power converted / power used

Multiple the result times 100 to convert the efficiency into a percentage.

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