Phys Ch 7

A

1. How long have electrostatic effects with amber been known? a. about 2500 years b. about 500 years c. about 200 years d. about 100 years

D

12. Which statement is true about the electric force between two charges represented by Coulomb's aw? a. It acts along the line connecting the charges. b. It only applies to point charges. c. It is repulsive if the charges are like. d. All of these.

A

10. What is the mathematical equation that represents Coulomb's law? a. b. c. d.

D

11. What are the correct units for the constant k in Coulomb's law? a. Nxm/C b. Nxm^2/kg^2 c. Nxm^2/C d. Nxm^2/C^2

D

13. Which statement is true about the two electric forces associated with two electric charges? a. They are calculated using the sign of the charge in Coulomb's law. b. They are both in the same direction if the charges are like. c. They are both in the same direction if the charges are unlike. d. They form an equal and opposite pair according to Newton's third law of motion.

C

14. Two identical electric charges q1 and q2 are separated by a distance r. If r is tripled, what happens to the electric force between them? a. triples b. decreases by a factor of 3 c. decreases by a factor of 9 d. increases by a factor of 9

C

15. How can the electric force between two charges and be doubled? a. double both charges b. double the distance between the charges c. double just one of the charges d. cut the distance between the charges in half

A

16. The total force acting on a charge by other charges around it is the vector sum of the forces exerted by each of the charges. What is this rule known as? a. the superposition principle b. the law of electric charges c. Coulomb's law d. the inverse-square law

D

17. Which of the following is an example of a device that uses electric fields? a. a cellphone b. an X-ray machine c. a liquid crystal display d. all of these

B

18. Which fact is true about an electric field? a. It is always created by a single point charge. b. It can be represented as a collection of vectors at all points in space. c. It exerts a force on any object with mass. d. All of these.

A

19. Which statement is true about the electric field at a point in space? a. It points in the same direction as the force on a small positive test charge. b. It points in the same direction as the force on a small negative test charge. c. It points opposite to the direction of the force on a small positive test charge. d. It is not related to the force on a test charge.

B

2. Which statement is true? a. All protons carry the same amount of negative charge. b. Like charges repel and unlike charges attract. c. All electrons carry the same amount of positive charge. d. All of these.

A

20. An electric field is created by a point charge . A small positive test charge is a distance r from . What is the equation that gives the magnitude of the electric field at the location of the small test charge? a. elipson = kq2/r^2 b. elipson = kq2/r c. elipson = kq1/r^2 d. elipson = kq1/r

C

21. The magnitude of the electric field a distance r from a point charge q is . What is the magnitude of the magnetic field a distance of 2r from a particle of charge 3q? a.1/4elipson b.1/2elipson c.3/4elipson d.elipson

D

22. Which statement is true about electric field lines? a. They show the magnitude of the electric field. b. They are directed away from negative charges. c. They exist even in empty space far from any charges. d. They show the direction of the electric field.

C

23. Which statement correctly describes the density of electric field lines? a. The density increases with separation from a point charge. b. The density is proportional to the magnitude of the electric force. c. The density decreases with distance from a point charge. d. The density decreases when approaching a negative point charge.

A

24. Which statement describes an electric dipole? a. A dipole consists of two equal and opposite charges separated by a small distance. b. A dipole consists of two negative charges separated by a small distance. c. A dipole consists of two positive charges separated by a small distance. d. All of these.

C

25. Which statement describes the behaviour of a charged particle in an electric field? a. It remains at rest. b. It always accelerates in the direction of the field. c. It accelerates in the direction of the field if it is positively charged. d. It does work on the electric field as it accelerates.

B

26. A uniform electric field has a strength of 150 N/C. A charge of 1.20 C is placed in the field. How much work does the field do on the charge in moving it 0.500 m? a. The charge does work on the field. b. 360 J c. 180 J d. 75 J

C

27. A electric charge moves through an electric field from point P to point Q in a straight line through a distance, d. The field does 24.0 J of work on the charge. Suppose that the charge moved along a different path from A to B through a distance of 2d. What is the work done in this case? a. 0 J b. 12.0 J c. 24.0 J d. 48.0 J

A

28. A charge is at vertex A of a hexagon ABCDEF. The charge is in an electric field with uniform strength . The charge moves from point A to point D. Which path results in the largest change in electric potential energy? a. All paths have the same change in electric potential energy. b. A-D c. A-B-D d. A-B-C-D

C

29. An electric field is created by a positive point charge Q. A test charge q is separated from the charge Q by a distance, r. How can the electrical potential energy of charge q be increased? a. Use a negative charge and letting it accelerate. b. Use a positive charge and letting it accelerate. c. Use a positive charge and moving it toward Q with an external force. d. Use a negative charge and moving it toward Q with an external force.

A

3. What is true concerning the total charge of a closed system? a. remains constant b. always neutral c. always positive d. always negative

B

30. A fixed negative charge Q creates an electric field. A positive test charge q is located a distance r from the field. The test charge is allowed to move freely. Which of the following statements is true? a. The electrical potential energy of q increases as it moves. b. The electrical potential energy of q decreases and the kinetic energy of q increases. c. The electrical potential energy of q increases and the kinetic energy of q decreases. d. The charge q does work on the field as it moves.

D

31. What is electric potential? a. the kinetic energy per unit charge b. the electric field strength per unit charge c. the work done per unit charge by an electric field d. the electric potential energy per unit charge

A

32. Which equation gives the electric potential due to a charge q at a distance r? a. v=kq/r b. v=kq/r^2 c. v=kq^2/r d. v=kq^2/r^2

A

33. The electric potential due to a unit charge q at a distance r is V. What is the potential due to a charge of 4q at a distance of 2r? a. 2V b. V c. 1/2V d. 1/4V

B

34. A point charge Q produces a potential V at a distance r. A positive test charge q is moved from r to a distance of 2r. Which is true about the difference in potential experienced by the test charge? a. It is positive if Q is positive. b. It is negative if Q is positive. c. It is negative if Q is negative. d. It is equal to zero.

A

35. What, by convention, is the reference point for the electric potential created by a point charge? a. zero potential at an infinite distance from the charge b. zero potential at a unit distance from the charge c. zero potential at any convenient distance from the charge d. any of these can be used

b

36. Two identical point charges q are separated by a distance r, and have an electrical potential energy . Each charge is doubled, and the distance between them reduced by half. What is the electric potential energy? a. 16E b. 8E c. 2E d. E

B

37. What is a possible unit for electric potential? a. J b. J/C c. C/J d. N m/C2

C

38. Point charge creates a potential at point P, and point charge creates a potential at point P. Which is true about the total electric potential at point P? a. equals b. equals c. equals d. cannot be determined without knowing the relative locations of the charges and the point P

C

39. Who first measured the fundamental unit of electric charge experimentally? a. Coulomb b. Einstein c. Millikan d. Newton

C

4. What is the basic SI unit of charge? a. newton b. electron c. coulomb d. proton

A

40. What did Millikan use to bring charged oil drops to rest? a. an electric microbalance b. a static electric field c. batteries of a fixed high voltage d. all of these

A

41. A charged oil drop is at rest between the plates of a Millikan apparatus. What forces must be included on a FBD of the oil drop? a. the electric and gravitational force b. the electric, gravitational and normal force c. the electric force only d. the gravitational force only

A

42. Two plates in a Millikan apparatus are charged to 900 V and separated by a distance of 1.50 cm. What is the magnitude of the electric field between the plates? a. 60 000 N/C b. 1350 N/C c. 600 N/C d. 13.5 N/C

D

43. In order to calculate the charge on an oil drop, what other quantity did Millikan need to measure? a. the voltage across the plates b. the separation of the plates c. the mass of the drop d. all of these

D

44. How did Millikan determine the mass of the oil drop? a. by measuring its mass with a spring balance b. by measuring its volume and density c. by measuring its weight d. by measuring its terminal velocity in air

D

45. Which of the following is true concerning an electron and a proton? a. they have the same mass b. they have the same radius c. they are identical except for the sign of the electric charge d. they have the same magnitude of electric charge

C

5. What is the charge on one electron? a. 1 C b. +1 C c. -1.602x10^-19 d. 1.602x10^-19

B

6. Which of the following is an example of a good conductor? a. glass b. copper c. wood d. amber

B

7. Which statement is true? a. A liquid cannot be a good conductor. b. Salt water is a good conductor. c. A gas cannot be a good conductor. d. An insulator must contain free electrons.

D

8. A charged balloon is held near a stream of water flowing from a faucet. It attracts the water. Why is the water attracted? a. The charge on the balloon transfers to the water molecules causing attraction. b. The water molecules are charged. c. The water molecules break into hydrogen and oxygen atoms when in the presence of a charged object. d. The object induces a charge separation in the water.

C

9. How is electric force different from gravitational force? a. Electric force is a contact force only. b. Gravitational force is repulsive only. The electric force may be either attractive or repulsive. c. Gravitational force is attractive only. The electric force may be either attractive or repulsive. d. The electric force becomes stronger as the separation between two charged points increases.