Data Sheet
-31-
28. Ohm’s Law
Using Ohm’s Law, the resistance of each part could be
calculated. Build the circuit shown on the left. In this circuit
the heart LED (69) and the lamp (76) are in series so they see
the same current. If you had a voltmeter and measured the
voltage drop across each component, you would see that the
voltage drop across the heart LED (69) is much greater than
the voltage drop across the lamp (76).
According to Ohm’s Law, V=I*R, where V stands for Voltage,
I stands for Current and R stands for Resistance. It has been
discussed that the heart LED (69) has a relatively high internal
resistance built into it to protect the LED from being damaged
by too much current owing through it. The lamp (76) does not
have as high an internal resistance. Since the heart LED (69)
and lamp (76) are in series, the current owing through each
will be the same. Thus, Ohm’s law tells us that the voltage drop
across the heart LED (69) will be greater than that across
the lamp (76) (assuming I is constant in Ohm’s law, a higher R
leads to a higher V). Because of the higher voltage drop across
the heart LED (69), there is not enough voltage across the
lamp (76) to make it light.
29. Advantages of Series Circuits
Build the circuit shown on the left. The heart LED (69) and
the star LED (70) are in series and thus are dim due to the
internal resistance in both LED modules limiting the current
in the circuit. Although dim, the LED modules do still light and
one of the benets of this series circuit is that it is drawing less
current so the batteries will not drain as quickly.