Electric Charges

Quiz

Multiple Choice

1. The diagram shows a device called an electroscope. What will happen when a charged object is placed near it

2. Which diagram is correct?

3. Which diagram is correct?

4. Which diagram is correct? First picture in each pair is a picture when the rod is moved towards the electroscope and the second picture shows what happens when the rod is taken away from the electroscope.

5. Which diagram is correct? First picture in each pair is a picture when the rod is moved towards the electroscope and the second picture shows what happens when the rod is taken away from the electroscope after it briefly touches the electroscope

True or False

1.The force between two charges is doubled when their separation distance is halved.

2. Only a few objects possess charges.

3. Negative charges are disappears when they meet a positive charge.

4. Positive charges are generally stronger than negative charges.

5. Negative charges tend to attract negative charges..

Essay (5 pts)

A light metal sphere is vertically suspended on a thread when a negatively charged rod is held close to it. The sphere is initially attracted to the rod, momentarily touches it, then is repelled by the rod. Explain the behavior of the sphere to a first year student.

Problem Solving (12 Points)

Determine the total force exerted by three charges Q1, Q2 and Q3 on q. Assume that the charges are fixed in their positions.

Q1 = +10CQ2 = -15CQ3 = +10Cq= -15C

Misconception Quiz on Electric

FieldClaire & Cha

1. What can we say about the electric field inside the two metal spheres with charges +15C and -15C.

a. The sphere with the positive charge will have a positive electric field while the sphere with the negative charge will have a negative electric field.

b. The spheres will have same magnitudes of electric field but will have different directions.

c. No electric field can be found inside both spheres.

d. The electric fields in both spheres are directed parallel to the spheres’ surfaces.

2. What can we say about the electric field inside the two metal spheres both with +15C charge.

a. The larger sphere will have a lesser electric field.

b. The spheres will have same magnitudes of electric field but will have different concentrations.

c. No electric field can be found inside both spheres.

d. The electric fields in both spheres are directed parallel to the spheres’ surfaces.

3. What can we say about the electric field inside the two metal shells with charges +15C and -15C.

a. The shell with the positive charge will have a positive electric field while the shell with the negative charge will have a negative electric field.

b. The shells will have same magnitudes of electric field but will have different directions.

c. No electric field can be found inside both shells.

d. The electric fields in both shells are directed parallel to the shells’ surfaces.

4. What can we say about the electric field inside the two metal shells both with +15C charge.

a. The larger shell will have a lesser electric field.

b. The shells will have same magnitudes of electric field but will have different concentrations.

c. No electric field can be found inside both shells.

d. The electric fields in both shells are directed parallel to the shells’ surfaces.

5. What can we say about the electric field inside the two metal objects both with +15C charge.

a. The metallic sphere will have a lesser electric field.

b. The objects will have the same magnitudes of electric field but will have different concentrations.

c. No electric field can be found inside both objects.

d. The electric fields in both objects are directed parallel to the objects’ surfaces.

6. In the metal object below, where can we find the greatest concentration of charges?

7. When a charge B enters a region where an electric field due to charge A exists,

a. The field does not change because the electric field is a property of space which only applies a force on charges.

b. The field changes because the charge B also has an electric field which interacts with the electic field of charge A.

c. The elctric field does not change because it is uniform in that region.

d. The electric of A changes but the electric field of B remains unchanged.

AB

8. The closer the point is to a particular charge, __________________.

a. The weaker the electric field is at that point.

b. The stronger the electric field is at that point.

c. The same amount of electric field is felt if a test charge is placed to any other point surrounding the charge.

d. The electric field cannot be determined.

9. Which of the following is not true about electric field lines?

a. It is perpendicular at any point in the direction of the electric field vector.

b. It always intersects the equipotential lines at right angle.

c. The electric force and electric field lines are always mutually perpendicular.

d. Electric field lines never intersect.

10. The electric field 20 mm from a charge compared to the electric field 10 mm from the charge is

a. stronger b. weakerc. just equald. Cannot be determined

11. Electric field lines

a. Leave negative charges and enter positive ones

b. Are close together where E is weak and far apart where E is strong

c. Have the same pattern around the charged metal sphere as they do around a point charge

d. Physically exist

12. If the electric field is due to a charge distribution in a given space, the total electric field at a certain point P is ________________.

a. just the algebraic sum of the fields due to each point charge in the distribution.

b. the vector sum of the fields at point P due to each point charge in the distribution.

c. just the vector sum of the fields due to the charges closer to the point P.

d. always equal to zero.

13. The strength of the electric field at a certain point surrounding the charge that created it is dependent on the

a. magnitude of the charge producing the electric field

b. separation distance between the charge and a certain point

c. Only ad. a and b