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Elementary Circuits
12 questions By Tony R. Kuphaldt
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Question 4 of 12
How could a battery, a light bulb, and some lengths of metal wire be used as a conductivity tester, to test the ability of different objects to conduct electricity?
Reveal answerThe following circuit would function as a simple continuity tester. Simply place the open wire ends in contact with the object to be tested, and the light bulb will indicate whether or not the object conducts electricity to any substantial degree:
Notes:Not only is this question an opportunity to solve a problem, but it lends itself well to simple and safe experimentation. Encourage students to build their own conductivity testers and test various substances with them.
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Question 5 of 12
Suppose we had a long length of electrical cable (flexible tubing containing multiple wires) that we suspected had some broken wires in it. Design a simple testing circuit that could be used to check each of the cable’s wires individually.
Reveal answer
Notes:A significant portion of electrical/electronic circuit problems are caused by nothing more complex than broken wire connections, or faults along the length of wires. Testing cables for wire breaks is a very practical exercise.
The same technique may be used to “map” wires from one end of a cable to the other, in the event that the wires are not color-coded or otherwise made identifiable.
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Question 6 of 12
What do the symbols with the question marks next to them refer to? In the circuit shown, would the light bulb be energized?
Reveal answerThese are ground symbols, and they can either refer to connections made to a common conductor (such as the metal chassis of an automobile or circuit enclosure), or the actual earth (usually via metal rods driven into the dirt).
Notes:Ask the students about the relative conductivities of metal chassis versus dirt (earth ground). Is a current pathway formed by two metal chassis grounds equivalent to a current pathway formed by two earth grounds? Why or why not? What conditions may affect these relative conductivities?
