Resistors
may be used to either change the voltages or
the currents in a circuit.
In
this section we will see how we can use resistors to
protect L.E.D's. This is achieved by the resistor limiting
the amount of current that can flow through the L.E.D. By
preventing too much current entering the L.E.D. we avoid
damaging it.
We can simply
say that a resistor 'resists' the battery's
attempts to push too much current around the circuit and
L.E.D.
L.E.D.
- Resistor Circuit Diagram

Notice
that the + side of the battery connects via the
resistor to the Anode (+ side) of the L.E.D..
Resistors
come in
many different types
and values- We need
to choose the right
one.
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There
are many different types of L.E.D. too as we have
seen and it is important to match them with the correct
value resistor.
-
If the
resistor value is too big, too little current will flow
in the circuit and the L.E.D. won't work.
-
If the
resistor value is too small, too much current will
flow, possibly damaging the L.E.D. permanently.
Resistors
are measured in Ohms ( )
- and this tells us its
resistance value. A resistor
can be smaller than1 ohm or
bigger than10,000,000 ohms.
Choosing
the right resistor for an L.E.D.
Q25,
Open
the L.E.D. Resistor link at the top of the screen.
An example Super Bright L.E.D. is shown. It needs the
correct protection resistor. (Information to help you
work out the required value resistor is provided).
Follow the instructions and write in the box below
the calculated value of resistor needed to protect the
"Super Bright L.E.D.". Please check your answer.
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Identifying
Resistors using Colour Codes
When
you need to identify a resistor of a particular
value, you will be able to use the coloured rings
or bands around its case to show
you.
To
help you understand how to do this; open
the"resistor codes" link at the top of the screen and
read the instructions carefully. Then answer the
following questions to check your understanding:-
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