Data Sheet

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15. Ohm’s Law
Using Ohm’s Law the resistance of each part could be
calculated. Build the circuit to the left and turn on the
switch (62). In this circuit the lamp (76) and the star
LED (70) are in series so they all 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 star LED (70) is much greater than the
voltage drop across the lamp (76). According to Ohm’s
Law, R = V÷I which means the internal resistance of
the star LED (70) is much greater than the internal
resistance of the lamp (76). The high internal resistance
of the star LED (70) is limiting the current in this circuit,
which is why the lamp (76) does not light. Each part is
designed using Ohm’s Law to perform best when they
have full battery voltage. Press the press switch (61)
to remove the resistance in the star LED (70) from the
circuit and now the lamp (76) lights.
16. Reed Switch Technology
Replace the press switch (61) with the reed switch
(83), turn ON the switch (62) and the star LED (70)
will light. Touching the reed switch (83) with the magnet
(7) eliminates the star LED (70) from the circuit (all the
current ows through the reed switch and not the star
LED (70) and makes the lamp (76) light. A reed switch
is typically made from two or more ferrous reeds (thin
strips) encased within a small glass tube-like envelope,
which become magnetized and move together or
separate when a magnetic eld is moved towards the
switch.