| 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
|
Just
Games
Key
stage 123
