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Semiconductors
Suggested answer
Activity 1
Using a multimeter (your school will have one) set to resistance; check the conductivity of a diode. To do this touch one of the probes to each end of the diode and check the meter. Reverse the probes and check again. Note your results.
Equipment
A multimeter is a common testing device used in electrical and electronics trades. The meter is able to test a range of electrical features such as both DC and alternating voltage, current and resistance.
Figure 1: Shows a typical multimeter used in schools.
Method
When a standard diode is tested for resistance the battery in the multimeter provides a current that will flow through the item being tested, to the other probe and back to the meter. Movement of the needle indicates the completed circuit.
Figure 2:Shows the probes attached to the leads of the diode.
When the diode is tested, as shown above, the needle moved across to the right side, indicating current flow. When tested as shown below the needle remained stationary. Note the diode has been reversed, as indicated by the polarity symbol (silver stripe).
Figure 3: Shows the probes attached to the opposite leads of the diode.
Conclusion
Current flows in one direction only through a diode.
The development of semiconductors has
been a steady process from the 1600s to the present day. To put this development
of semiconductor materials into historic perspective view this
timeline 
.
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