Test 1

Question 1

20. Would defining the charge on an electron to be positive have any effect on Coulomb’s law?

Answer 1

No, although the direction of the force vector would be reversed in systems with electrons, if all else remained the same

Question 2

21. An atomic nucleus contains positively charged protons and uncharged neutrons. Since nuclei do stay together, what must we conclude about the forces between these nuclear particles?

Answer 2

Solution
The force holding the nucleus together must be greater than the electrostatic repulsive force on the protons

Question 3

23. When measuring an electric field, could we use a negative rather than a positive test charge?

Answer 3

Solution
Either sign of the test charge could be used, but the convention is to use a positive test charge.

Question 4

25. If the electric field at a point on the line between two charges is zero, what do you know about the charges?

Answer 4

Solution
The charges are of the same sign

Question 5

28. Compare the electric fields of an infinite sheet of charge, an infinite, charged conducting plate, and infinite, oppositely charged parallel plates.

Answer 5

The infinite sheet of charge has E everywhere. The infinite charged parallel plates have E between them and E=0 everywhere else if they have opposite charges. The field outside an infinite charged conducting plate is E.
E= sigma/(epsilon knot)

Question 6

29. Describe the electric fields of an infinite charged plate and of two infinite, charged parallel plates in terms of the electric field of an infinite sheet of charge

Answer 6

same as28 but E= sigma/(2epsilon)

Question 7

30. A negative charge is placed at the center of a ring of uniform positive charge. What is the motion (if any) of the charge? What if the charge were placed at a point on the axis of the ring other than the center?

Answer 7

The motion is null if it were placed at the center. If it were placed on the axis, the charge would move along this axis back and forth in simple harmonic motion.

Question 8

32. Under what conditions, if any, will the trajectory of a charged particle not follow a field line?

Answer 8

In a uniform field, if released from rest or with an initial velocity already pointing along a field line.

Question 9

33. How would you experimentally distinguish an electric field from a gravitational field?

Answer 9

At the surface of Earth, the gravitational field is always directed in toward Earth’s center. An electric field could move a charged particle in a different direction than toward the center of Earth. This would indicate an electric field is present.