Chapter 4 Review

Video Review

Key Concept Summary

TA Summary


The basic positive charge-carrying particle in an atom.
Metal alloys that are attracted to magnets or are capable of being transformed into a permanent magnet.
A material that does not permit electrons to flow through it.
The matematical formula F = kqQ/d2 which describes the strength of the force between two objects of charge Q and q with their centers separated by the distance d.
A current of electrons that changes direction of flow.
The unit of measure for charge.
Material that allows electrons to flow through it.
The basic negative charge-carrying particle in an atom.
A steady flow of electrons in one direction through a wire.
A repulsive force between electrons near the surface of two different objects.
A number relating the strength of the electric force to the charges involved and their distance apart.
A neutral particle found in the nuclei of atoms.


Friction comes from electromagnetic forces.
Electric force becomes stronger if the charged objects are moved farther apart.
Neutrons have a negative charge
Iron and nickel are examples of ferromagnetic metals.
Electric currents exert forces on permanent magnets.


When a glass rod is rubbed with a rubber sheet, the glass rod becomes positively charged. This is because
Suppose you wanted to exactly double the electric force between two objects. How could you accomplish that?

Free Response

  1. Describe an experiment that demonstrates that there are two kinds of electric charge.
  2. Describe the differences between conductors and insulators.
  3. Describe the important properties of a proton and an electron. What is the comparison in sizes?
  4. What is electric current?
  5. How do we know that there is a single electromagnetic force rather than separate electric and magnetic interactions?
  6. What makes a material ferromagnetic?
  7. Explain how the contact and friction forces arise and play an important role in the following scenarios:
    • A book placed on a table.
    • A car tire screeching to a stop at a cross walk to avoid hitting pedestrians.
    • A space shuttle reentering Earth’s atmosphere.
    • A water skier gliding across the water.
  8. A rubber rod is rubbed with fur and suspended in the air. A second rubber rod that has been rubbed with fur is placed nearby.
    • What charges are on the rubber rods?
    • Do the rods attract or repel one another?
    • What law explains why this occurs?
    • As you bring the rubber rods closer together, what happens to the force between them?
    • What could you do to decrease the force between the rods, without changing the distance?
    • If you replaced one of the rubber rods with a glass rod that had been rubbed with silk, how would your answers to the above questions change?
  9. Three spheres of metal are placed on stands that act as insulators. Spheres B and Y are neutrally charged. Sphere U holds a strong negative charge. Wire runs between sphere B and Y. Sphere U is brought close to sphere Y.
    • Because spheres B and Y hold no net charge, does that mean that no charge exists on them?
    • What do we know about the amount of negative and positive charge in spheres B and Y?
    • What will sphere U do to the electrons in sphere Y as it approaches?
    • What does this do to the net charge on sphere Y?
    • What does this do to the net charge on sphere B?
    • How is it possible for charge to arise from two neutrally charged objects?
  10. Describe two ways in which you could turn iron wire into a magnet. Only one of these two methods would work with copper wire. Which one and why?
  11. If you scuff across wool carpet wearing rubber shoes, you will shock yourself when you reach for a metal doorknob, often before you even touch the knob.
    • What type of charge will have accumulated on your body? How do you know?
    • When you bring your finger near the doorknob, what happens to the electrons in the metal?
    • Explain why, when the metal itself is neutral, a spark will often jump from your finger to the metal before you touch it.