Experiments with Static Electricity

1. On the Gizmo, click Show force vector for charge A and Show force vector for charge B. The forces on each charge are represented by the purple and green arrows. The charges of each particle, qA and qB, are shown below the particles. Check that each charge is set to10.0 • 10−4 C.
a. Observe the arrows representing the Coulomb force between the charges. Do you think this represents an attractive or a repulsive force?
Ans. Repulsive force
b. Change the charge of particle A (qA) to -10.0. (To change qA, type a value in the field next to the slider and hit Enter.) You now have a positive and a negative charge (as in the "hair and balloon" experiment). What effect does this have on the arrows? Is this an attractive or repulsive force?
Ans. Attractive force
c. Change the charge of particle B to -10.0. What kind of force is experienced by two negative charges? You can model this by rubbing two balloons and slowly bringing them together.
Ans. It is a repulsive force because they are not opposites
d. Change the charge of particle A back to +10.0. As a rule, what kind of force will result when charges are opposite? What kind of force will result when the particles have the same charge?
Ans. The charges are opposite so they will attract
2. Change the charge of particle A to 0.0. A particle with zero charge is neutral.
a. What happens to the force arrows?
Ans. The arrows are not there any more
b. What is the force between a charged particle and a neutral particle? Try several values for particle B to see if this is always true. (Note: In reality, neutral objects are composed of charged particles. If you bring a charged object near a neutral object, the charged particles within the neutral object will rearrange themselves in a process calledpolarization. This results in an attractive force between the charged object and the neutral object that is not shown in the Gizmo.)
Ans. There is no force
3. To see the magnitude of the Coulomb force, click Show vector notation for particle A and particle B. The magnitude of the force (in Newtons) is written |FA| or |FB|. Set each charge to 10.0 • 10−4. Click Show distance and Show grid, and drag the particles together until the distance between them is 30 m.
a. What is the Coulomb force on particle A?
Ans. 10n
b. What is the force on particle B?
Ans. 10n
c. Drag the particles around. Are the forces on particle A and B always equal to one another?
Ans. Yes


4. Before altering the charges, write a hypothesis in your notes. What do you think the force will be if one of the charges is halved? When you have written your prediction, change the charge of particle A to 5.0 • 10−4 C and press Enter.
a. What is the force on the particles now? Does this agree with your hypothesis?
Ans. The force has decreased to 2.81 and that doesn’t agree with my hypothesis
b. Change the charge of particle B to 5.0 • 10−4 C. What is the force now?

Ans. It has decreased to 1.41
c. Try several other combinations of charges. (Stick with whole numbers so it is easier to see the relationship.) What pattern do you see?
Ans. The larger the charges, the larger the force