Physical Effects of Electricity

Basic Electricity

• Question 1

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.

• Question 2

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?

• Question 3

How long will it take for the light bulb to receive electrical power once the battery is connected to the rest of the circuit?

• Question 4

A 22-gauge metal wire three feet in length contains approximately 28.96 ×1021 “free” electrons within its volume. Suppose this wire is placed in an electric circuit conducting a current equal to 6.25 ×1018 electrons per second. That is, if you were able to choose a spot along the length of this wire and were able to count electrons as they drifted by that spot, you would tally 6,250,000,000,000,000,000 electrons passing by each second. (This is a reasonable rate for electric current in a wire of this size.)

Calculate the average velocity of electrons through this wire.

• Question 5

In the late 1700’s, an Italian professor of anatomy, Luigi Galvani, discovered that the leg muscles of a recently deceased frog could be made to twitch when subjected to an electric current. What phenomenon is suggested by Galvani’s discovery? In other words, what does this tell us about the operation of muscle fibers in living creatures? More importantly, what practical importance does this have for people working near electric circuits?

• Question 6

Paramedics and other emergency medical personnel sometimes use a machine called a defibrillator to re-start the regular heart-beat of a person whose heart has stopped or is spastically convulsing (fibrillating). Explain what this machine does to “restart” a person’s heart.

• Question 7

What difference will it make if the battery in this circuit is reversed in direction?

• Question 8

What physical effects of electricity are manifest in a lightning strike?

• Question 9

If the terminals of a DC voltage source are connected to individual wires, dipped in a container full of water, an interesting effect takes place on the submerged surfaces of the wires. What is this phenomenon, and what is it called?

• Question 10

What effect takes place when an electric current passes through a coil of wire, wrapped around an iron object such as a large-diameter bolt? Hint: place some small paperclips or other lightweight steel objects near the end of the bolt when energizing the coil. What is this phenomenon called?