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13
Project #7
Build the circuit shown on the left by placing all the parts with a black 1
next to them on the base grid rst. Then, assemble parts marked with a 2.
When you close the slide switch (S1), current ows from the batteries
(B1) through the slide switch, through the resistor (R1), through the
LED (light emitting diode, D1) and back to the battery. The closed slide
switch completes the circuit. The resistor limits the current and prevents
damage to the LED. NEVER PLACE AN LED DIRECTLY ACROSS THE
BATTERY! If no resistor is in the circuit, the battery may push enough
current through the LED to damage the semiconductor that is used to
produce the light. LEDs are used in all types of electronic equipment to
indicate conditions and pass information to the user of that equipment.
Can you think of something you use everyday that has an LED in it?
Light Emitting Diode
OBJECTIVE: To show how a resistor and LED are wired to
emit light.
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Project #8
Rebuild the circuit from Project #7 but leave the slide switch (S1) out as
shown on the left.
When you place a metal paper clip across the terminals as shown in
the picture on the left, current ows from the batteries (B1) through the
resistor (R1), through the LED (D1), and back to the battery. The paper
clip completes the circuit and current ows through the LED. Place your
ngers across the terminals and the LED does not light. Your body has
too high of a resistance to allow enough current to ow to light the LED.
If the voltage, which is electrical pressure, was higher, current could be
pushed through your ngers and the LED would light. This detector can
be used to see if a material like plastic is a good conductor or a poor
conductor.
Conduction Detector
OBJECTIVE: To make a circuit that detects the conduction of
electricity in different materials.
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