Question

chapter 20 electricity
match each material to the category of a conductor or insulator.
material category

1. copper a. conductor
2. plastic b. insulator
3. rubber
4. silver
5. wood

resistance (page 605)

1. explain why the current is reduced as electrons move through a conductor.
2. circle the letter of each factor that affects a materials resistance.

a. its length b. its temperature
c. its velocity d. its thickness

1. what is a superconductor?

Explanation:

• For the matching part (7 - 11):
• Copper and silver are metals. Metals have free electrons that can move easily, so they are good conductors of electricity.
• Plastic, rubber, and wood do not have free electrons that can move easily to conduct electricity, so they are insulators.
• For question 12:
• As electrons move through a conductor, they collide with the atoms and ions in the conductor. These collisions impede the flow of electrons. According to Ohm's law \(I=\frac{V}{R}\) (where \(I\) is current, \(V\) is voltage, and \(R\) is resistance), an increase in resistance (due to collisions) for a constant voltage will reduce the current.
• For question 13:
• The formula for resistance \(R =

ho\frac{l}{A}\) (where \(
ho\) is resistivity, \(l\) is length, and \(A\) is cross - sectional area which is related to thickness) shows that length and thickness (through cross - sectional area) affect resistance. Also, temperature affects the resistivity \(
ho\) of a material. Velocity is not a factor in the basic formula for resistance of a material.

• For question 14:
• A superconductor is a material that has zero electrical resistance below a certain critical temperature. This means that electric current can flow through it without any loss of energy due to resistance.

Answer:

1. a. conductor
2. b. insulator
3. b. insulator
4. a. conductor
5. b. insulator
6. Electrons collide with atoms/ions in the conductor, increasing resistance. For constant voltage (\(V\)), using \(I = \frac{V}{R}\), higher \(R\) means lower \(I\).
7. a. its length, b. its temperature, d. its thickness
8. A material with zero electrical resistance below a critical temperature.