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Physical Effects of Electricity
11 questions By Tony R. Kuphaldt
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Question 1 of 11
Certain substances are known to physically deform (shorten or lengthen) when an electrical voltage is applied across their length. The effect is known as piezoelectricity. What types of substances are known to be piezoelectric? Identify some possible applications of this phenomenon.
Reveal answerCertain crystal substances, such as quartz, are known to be piezoelectric.
Notes:As your students will no doubt discover in their research, piezoelectricity is a two-way effect: physical motion from electricity and visa-versa. It will be clear how well they did their research by the types of applications they think of for the “electricity-to-motion” form of piezoelectricity, given the typical physical scale of piezoelectric displacements.
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Question 2 of 11
When an electric current passes through a conductor offering some electrical resistance, the temperature of that conductor increases above ambient. Why is this? Of what practical importance is this effect?
Reveal answerElectrical resistance is analogous to mechanical friction: electrons cannot freely flow through a resistance, and the “friction” they encounter translates some of their energy into heat, just as the friction in a worn mechanical bearing translates some of the kinetic energy of it’s rotation into heat, or the friction between a person’s hands while rubbing them together on a cold day translates some of the motion into heat.
Notes:This is a good starting point for a discussion on work, energy, and power. Power, of course, may be directly calculated by multiplying voltage by current, and is measured in watts. It also provides an opportunity to discuss some of the practical limitations of electrical conductors.
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Question 3 of 11
How long will it take for the light bulb to receive electrical power once the battery is connected to the rest of the circuit?
Reveal answerApproximately 11 milliseconds (0.0107 seconds).
Notes:Electricity is fast: the effects of electron motion travel at approximately the speed of light (186,000 miles per second). Actual average electron velocity, on the other hand, is very, very slow. A convenient analogy I’ve used to illustrate how electrons may move slowly yet have rapid effect is that of a closed-loop hydraulic system. When the valve is opened, fluid motion throughout the system is immediate (actually, the motion progresses at the speed of sound through the fluid - very fast!), yet the actual velocity of fluid motion is much slower.
Incidentally, the double-chevron symbols indicate an electrical connector pair (plug and jack; male and female).
