GCSE Electronics

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Ohms laws
A simplified explanation

Preview  of Basic Electricty

One the most important and fundamental laws of electronics is that of ohms law.

This law defines the relationships between current, voltage and resistance.

A good way to understand ohms laws is an analogy with a domestic water system.

The same way that an electric current flows through a copper wire, water flows through a copper pipe in a water system.

Most people do not think to much about the fact but when they turn on tap the water comes out as a result of the pressure that is provided  by a pumping station some miles away.

This water pressure is similar to that used to drive electricity around a circuit, the potential difference or pd for short is the term that is used - this is measured in volts.

This driving force is provided by a battery or in the case of mains electricity a generator at the power station

Definition of 1 Volt

The unit of electromotive force or electric pressure. It is the electromotive force(pd) which, if steadily applied to a circuit having a resistance of one ohm, will produce a current of one ampere

The water that flows through a copper pipe  can be considered similar to that which flows through an electric cable.

The current flow in a cable cannot of course come out of the cable like water can leak out of pipes or come out of the tap

However a force is required to drive it and resistance to this flow is encountered, the flow of current is measured in amps 

Definition of 1 Amp

The standard unit of electric current. The current produced by a pressure of one volt in a circuit having a resistance of one ohm

An amp is quite a large measure of current flow and you will probably find that most circuits will have milliamps flowing through them - that is one thousands of an amp.

When water or an electric current flows  then a resistance to that flow is encountered, the measurement of resistance is an ohm

Definition of 1 Ohm

The unit by which electrical resistance is measured. One ohm is equal to the current of one ampere which will flow when a voltage of one volt is applied

Now that you are aware of what a ohm, volt and amp are - I shall introduce you to the mathematical relationship that is ohms law.

Definition of Ohms Law

the principle that the electric current passing through a conductor is directly proportional to the potential difference across it, provided that the temperature remains constant. The constant of proportionality is the resistance of the conductor 

The definition above is quite a mouthful, it simply states that the current passing through a conductor increases if you increase the voltage 

Obvious really - increase the pressure (voltage) and you will find more current will flow. 

All circuits have a certain degree of opposition (resistance) to current flow through them, the relationship is given by R=V/I, 

An increase in current flow with the same voltage will assume an decrease in resistance 

The above triangle allows the student to calculate any of the 1 of the 3 variables if the other 2 are known.

Cover the variable that you require and perform the resulting calculation.

Consider the circuit shown below

The resistance of that circuit would be given by R=V/I  24/2 = 12 ohms

The current flowing through the circuit would be given by  V/IR 24/12 = 2amps

The voltage would be given by I x R  2 x 12 = 24 volts

If you continue your studies to a more advanced level than GCSE then you will find that ohms law is one of the most fundamental electronics laws


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