Electricity Chapter 2

What happens to electrons in a conductor when a voltage is applied?

• The electrons flow toward the negative terminal of the voltage source.
• The electrons drift away from the nuclei and float around in all directions.
• The electrons flow toward the positive terminal of the voltage source.
• The electrons flow back and forth between the positive and negative terminals of the voltage source.

you learned that a conductor is a material that passes electrons easily and that an insulator is a material that does a poor job of conducting (or passing) electrons. How are the electrons in an insulator different from the electrons in a conductor?

• There are no electrons present in insulating materials.
• The electrons in an insulator are tightly bound to the positively charged nucleus.
• 
  The electrons in an insulator are bound loosely to the positively charged nucleus.
• The electrons in an insulator flow toward the negative terminal.

An MRI machine uses electricity to create a very strong magnetic field, which is used to form images of tissues inside the human body. In order to create this powerful electromagnet, electrons must experience almost no resistance while passing through the wiring. This can be accomplished through the use of a(n)

• semiconductor
• conductor
• insulator
• superconductor

Suppose you wanted to design a light bulb that produces a bright light using a small amount of current. Which material would best serve this purpose?

• a filament with high resistance
• 
  a filament with low resistance
• a filament with no resistance
• a filament with complete resistance

Some lights are controlled by dials rather than by switches. These dials are called dimmer switches and turning the dial controls the brightness of the light. This type of device is called a

• resistor
• conductor
• controller
• rheostat

Resistance is a measure of how difficult it is for electrons to flow through a substance.

• True 
• False

When a switch is turned on, two conductors are pressed together.

• True 
• False

You have learned that resistance in a wire changes with both the length and diameter of the wire. Which wire would offer the most resistance to an electrical current?

• 
  a wire that is 50 cm long and has a diameter of 1.5 mm
• a wire that is 25 cm long and has a diameter of 1.5 mm
• a wire that is 50 cm long and has a diameter of 3 mm
• a wire that is 25 cm long and has a diameter of 3 mm

Resistance within a conductor changes with temperature. Which example given below would have the greatest resistance?

• a light bulb filament with 10 A of current running through it at 5°C
• a light bulb filament with 20 A of current running through it at 20°C
• a light bulb filament with 20 A of current running through it at 5°C
• a light bulb filament with 10 A of current running through it at 20°C

Your teacher asks you to measure the electric current passing through a circuit consisting of a 9-V battery, a small electric motor, and some copper wire. Which device would you use to carry out this task?

• a voltmeter
• 
  an ammeter
• a current detector
• an ohmmeter