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Specific Resistance of Conductors
15 questions By Tony R. Kuphaldt
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Question 13 of 15
What size (gauge) of copper wire is needed in this circuit to ensure the load receives at least 110 volts?
Reveal answer#6 gauge copper wire comes close, but is not quite large enough. #5 gauge or larger will suffice.
Notes:Several steps are necessary to solve this problem: Ohm’s Law, algebraic manipulation of the specific resistance equation, and research into wire sizes. Be sure to spend adequate time discussing this problem with your students!
The concept of a generic “load” is any component or device that dissipates electrical power in a circuit. Often, generic loads are symbolized by a resistor symbol (a zig-zag line), even though they might not really be a resistor.
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Question 14 of 15
A strain gauge is a type of sensing device widely used in the aerospace industry, for testing of vehicles and mechanical components. Explain what a strain gauge does, and how it functions.
Reveal answerA strain gauge converts micro-mechanical motions (“strain”) into electrical resistance changes. Typically, strain gauges are used to measure the stretching, compressing, and twisting of metal components under stress.
Notes:Ask your students to relate their answers to the illustration shown in the question. How does that strange-looking device actually measure strain? How does its resistance change, and why?
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Question 15 of 15
How does the conductance (G) of a conductor relate to its length? In other words, the longer the conductor, the (fill-in-the-blank
) its conductance is, all other factors being equal.
Reveal answerConductance decreases as length increases, all other factors being equal.
Follow-up question: how does “conductance” (G) mathematically relate to resistance (R), and what is the unit of measurement for conductance?
Notes:There are two units of measurement for conductance: the old unit (which makes perfect sense, even though your students may laugh at it, at first), and the new unit (named after a famous electrical researcher). Make sure your students are familiar with both.
