Elenco Basic Electronic Experiments - Manual (Page 24)

TEST YOUR KNOWLEDGE #1
1. __________ are the particles that flow between atoms as part of an electric current.
2. A __________ circuit occurs when wires or components from different parts of the circuit accidentally connect.
3. A __________ produces electricity using a chemical reaction.
4. To decrease the current in a circuit you may decrease the voltage or __________ the resistance.
5. Materials which have very high resistance are called __________ and materials which have very low resistance are
called __________.
6. Adding resistors in parallel __________ the resistance while adding resistors in series _________ the resistance.
7. The electrical resistance of water __________ when salt is dissolved in it.
8. Capacitors are components that can store __________ for periods of time.
9. Capacitors have low resistance to __________ current and high resistance to __________ current.
10. Adding capacitors in parallel __________ the capacitance while adding capacitors in series __________ the
capacitance.
(Answers are on page 3)
INTRODUCTION TO DIODES
The Diode: The diode is an electronic device that allows current to flow in only one direction. In our water pipe analogy it
may be thought of as the check valve shown here:
The check valve only allows water to flow in one direction, to the right in this drawing. There is a small spring and if the
water pressure exceeds a certain level then the spring will be stretched and the valve opened. If the pressure is to flow to
the left then the plate will be pressed against the solid stop and no water will flow.
Electronic diodes are made from materials called semiconductors, so-called because they have more resistance than
metal conductors but less than insulators. Most semiconductors are made of Silicon but Gallium Arsenide and Germanium
are also used. Their key advantage is that by using special manufacturing processes their resistance is decreased under
certain operating conditions. The manufacturing processes create two regions of permanent electrical charge, quite
different from charging a capacitor. While the physics of how this works is quite complicated, the effect is that once the
voltage across the diode exceeds a small turn-on level (0.7V for Silicon) the resistance of the diode becomes very low in
one direction (so low in fact that the current flow must be limited by other resistances in the circuit to prevent damage to
the diode). When the diode is turned on like this we refer to it as being forward-biased. In the other direction the diode
is always a very high resistance, we call this reverse-biased. The schematic symbol, shown below, indicates that the diode
will allow current to flow from left to right but block current flow from right to left.
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Solid Stop
Water-Tight Pivot
Movable Plate
Spring
DIODE Symbol for DIODE