Physics 2 review, Ch. 19, Chapter 19 Reading Questions, ch18, Physics 181., Chap 18 Conceptual Questions, Chapter 18: Magnetic Stuff

What is the electric potential energy of a +3.0 μC charge placed at corner A?

(for the 4-corner drawing of a square)

0.18 J

What is the magnitude of the electric field at P, the center of the square?

zero V/m

What is the electric potential at P, the center of the square?

4kQ/a

Determine the electric potential at the point P.

(Two Charges of opposite sign and equal magnitude Q=2.- C are held 2 m apart.)

zero volts

How much work is required to move a 1.0 C charge from infinity to the point P?

zero joules

Which one of the following statements concerning electrostatic situations is false?

No force component acts along the path of a charge as it is moved along an equipotential surface.

A charge is located at the center of sphere A (radius RA = 0.0010 m), which is in the center of sphere B (radius RB = 0.0012 m). Spheres A and B are both equipotential surfaces. What is the ratio VA/VB of the potentials of these surfaces?

1.2

A point charge gains 50 μJ of electric potential energy when it is moved from point D to point G. Determine the magnitude of the charge.

1.3 μC

The magnitude of the charge on the plates of an isolated parallel plate capacitor is doubled. Which one of the following statements is true concerning the capacitance of this parallel-plate system?

The capacitance remains unchanged.

A parallel plate capacitor with plates of area A and plate separation d is charged so that the potential difference between its plates is V. If the capacitor is then isolated and its plate separation is decreased to d/2, what happens to its capacitance?

The capacitance is twice its original value.

A parallel plate capacitor is fully charged at a potential V. A dielectric with constant κ = 4 is inserted between the plates of the capacitor while the potential difference between the plates remains constant. Which one of the following statements is false concerning this situation?

The electric field between the plates increases by a factor of four.

Which one of the following changes will necessarily increase the capacitance of a capacitor?

placing a dielectric between the plates

Complete the following statement: When a dielectric with constant κ is inserted between the plates of a charged isolated capacitor

the electric field between the plates is reduced by a factor of κ.

A parallel plate capacitor has a potential difference between its plates of 1.6 V and a plate separation distance of 2.5 mm. What is the magnitude of the electric field if a material that has a dielectric constant of 3.4 is inserted between the plates?

190 V/m

The effective area of each plate of a parallel plate capacitor is 2.1 m2. The capacitor is filled with neoprene rubber (κ = 6.4). When a 6.0-V potential difference exists across the plates of the capacitor, the capacitor stores 4.0 µC of charge. Determine the plate separation of the capacitor.

1.8 ◊ 10-4 m

A uniform electric field of 8 V/m exists between the plates of a parallel plate capacitor. How much work is required to move a +20 μC point charge from the negative plate to the positive plate if the plate separation is 0.050 m?

8 ◊ 10-6

A capacitor is initially charged to 3 V. It is then connected to a 6 V battery. What is the ratio of the final to the initial energy stored in the capacitor?

9

A potential difference of 120 V is established between two parallel metal plates. The magnitude of the charge on each plate is 0.020 C. What is the capacitance of this capacitor?

170 µF

The plates of a parallel plate capacitor each have an area of 0.40 m2 and are separated by a distance of 0.02 m. They are charged until the potential difference between the plates is 3000 V. The charged capacitor is then isolated.

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Determine the magnitude of the electric field between the capacitor plates.

1.5 ◊ 105 V/m

The plates of a parallel plate capacitor each have an area of 0.40 m2 and are separated by a distance of 0.02 m. They are charged until the potential difference between the plates is 3000 V. The charged capacitor is then isolated.

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Determine the value of the capacitance.

1.8 ◊ 10-10 F

The plates of a parallel plate capacitor each have an area of 0.40 m2 and are separated by a distance of 0.02 m. They are charged until the potential difference between the plates is 3000 V. The charged capacitor is then isolated.

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Determine the magnitude of the charge on either capacitor plate.

5.4 ◊ 10-7 C

The plates of a parallel plate capacitor each have an area of 0.40 m2 and are separated by a distance of 0.02 m. They are charged until the potential difference between the plates is 3000 V. The charged capacitor is then isolated.

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How much work is required to move a -4.0 μC charge from the negative plate to the positive plate of this system?

-1.2 ◊ 10-2 J

The plates of a parallel plate capacitor each have an area of 0.40 m2 and are separated by a distance of 0.02 m. They are charged until the potential difference between the plates is 3000 V. The charged capacitor is then isolated.

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Suppose that a dielectric sheet is inserted to completely fill the space between the plates and the potential difference between the plates drops to 1000 V. Determine the dielectric constant.

3.0

Electric potential energy is defined in a similar manner to the gravitational potential energy. Complete the following statement: These two potential energies are analogous to each other in that

both the electric and gravitational forces can be either attractive or repulsive forces.

A positively-charged particle is held at point A between two parallel metal plates. The plate on the left has a net positive charge +q and the plate on the right has a net negative charge -q. The particle is then moved to point B which is far from other charges. How does the electric potential energy at point A compare with that at point B?

EPEA > EPEB

Which of the following choices represents the quantity that is equal to the electric potential?

EPE/q0

Which of the following units are the SI units for the electric potential?

volt (v)

Points A, B, and C lie along a line from left to right, respectively. Point B is at a lower electric potential than point A. Point C is at a lower electric potential than point B. Which one of the following statements best describes the subsequent motion, if any, of a positively-charged particle released from rest at point B?

the particle will accelerate in the direction of point C

What is the name of unit of energy that is the amount by which the electric potential energy of an electron changes when it moves through a potential difference of one volt?

electron volt (eV)

A conducting sphere is connected via a wire to the ground. For a very short time, electrons move from the ground to the sphere. Then, no more electrons move to the sphere. Complete the following sentence: Before the wire was connected, the sphere's electric potential had a

positive value

Which one of the following phrases best describes the electric potential of a charged particle?

the potential energy per unit charge

Point charge A is located at point A and point charge B is at point B. Points A and B are separated by a distance r. To determine the electric potential at the mid-point along a line between points A and B, which of the following mathematical approaches is correct?

The algebraic sum of the two electric potentials is determined at a distance r/2 from each of the charges, making sure to include the signs of the charges.

Consider the two charged particles situated as follows: One charge located on the y axis has a value -2q and is located at a distance r from the origin, point O. The other charge has a value -q and is located at a distance 2r from the origin along the x axis. Which one of the following statements concerning the electric potential at the origin is true?

the total electric potential at the origin is equal to -5kq/2r

Which one of the following statements concerning equipotential surfaces is true?

The net work done by electric forces that move a charge along an equipotential surface is equal to zero joules.

Which one of the following statements concerning equipotential surfaces is false?

a) All points on an equipotential surface have the same electric potential. b) No work is done by the net electric force as a charge moves from one equipotential surface to another. c) The electric field created by one or more charges is everywhere perpendicular to the associated equipotential surfaces. d) The electric field created by one or more charges points in the direction of decreasing potential. e) There is a quantitative relationship between the electric field and the associated equipotential surfaces that surround one or more charges.

No work is done by the net electric force as a charge moves from one equipotential surface to another

What happens to a capacitor when an insulator is inserted between he two conductors of the capacitor?

the capacitance of the capacitor increases

A battery charges capacitor A until the potential difference between the two conductors of the capacitor is V. A second, identical capacitor, labeled B, is charged by another battery until the potential difference of capacitor B is 2V. How does the stored energy of capacitor B compare to that of capacitor A?

the stored energy of capacitor B is four times that of capacitor A

Which of the following changes would result in an increase in the energy stored in a parallel-plate capacitor, assuming all other variables remain constant?

a) insert an insulator between the plates b) increase the distance between the plates c) decrease the distance between the plates d) increase the area of the plates

None of the changes listed above will change the energy stored in the capacitor

Which one of the following choices is the unit for capacitance

a. sievert

b. farad

c. mho

d. joule

e. electron volt

b. farad

Which is a working definition of capacitance?

the amount of charge needed to produce a certain potential difference across a capacitor

Which one of the following is a primary consideration in determining the capacitance of a parallel-plate capacitor?

the size and separation of the plates

When the distance between charged parallel plates of a capacitor is d, the potential difference is V. If the distance is decreased to d/2, how will the potential difference change, if at all?

the new potential difference would be twice the previous value

an electrically isolated object is electrically neutral. what is the charge on object if 3 electross removed?

+3e

nitrogen atom's nucleus has 7 protons? how many electrons does an electrical neutral nitrogen atom have?

7

an electrically neutral ballon is rubbed on cloth and becomes positively charged. what can be said about its mass?

A. no change

B. increases

C. decreases

C. mass decreases

Suppose an electron is moving with a constant velocity until it encounters a positively charged sphere on it right. how does the sphere alter the trajectory of the electron?

A. has no effect on electron's trajectory

B. deflects electron to right

C. deflects electron to left

D. impossible to tell

B. deflects electron to right

which one of the following is a good conductor?

A. cloth

B. glass

C. wood

D. lead

if you place a large number of electrons in one small spot on a conductor, they immediately redistribute themselves on the surface because they repel one another. what happens if you place a large number of electrons in one small spot on the surface of an insulator?

A. they immediately redistribute themselves on the surface of the insulator because they repel one another

B. They stay in the area in which they are initially deposited for a relatively long time because they are not free to move about the insulator

C. they immediately redistribute themselves through the entire volume of the insulator because they repel one another

electrical charge not only lives in an _______ but also _______ an objects

1. objects

2. moves through

material differ in their abilities to what regarding electric charge?

material diff in abilitiies to allow electirc charge (conduct) move thru them

metals conduct heat _____. This makes them thermal ______.

1. readily

2. conductors

substance that conduct heat poorly are known as?

thermal insulators

good conductors

copper, gold, iron salwater

good insulators

plastic, rubber, glass, wood

good thermal conductors are good ______ conductors

electrical

these readily move electric charge

electrical conductors

good thermal conductors are generally good _______ (some exceptions!)

electrical conductors (exception)

T/F: electrons move freely in insulators

FALSE

these dont conduct electricity, electrons are bound

electrical insulators

within these electrons move freely, they can . . . electricity

conductors

example of electrical insulator

rubber around wires prevent electrical charge going where not wanted

the difference between electrical conducts versus insulators is related to _____

atomic structure

(as electrons orbit nucleus, those in outer orbits experience weaker attraction to nucleus than those in inner orbits)

valenece electrons dislodged ______ easily than inner ones do

more

1. Which one of the following statements best explains why tiny bits of paper are attracted to a charged rubber rod?

C) The paper becomes electrically polarized by induction.

2. Five styrofoam balls are suspended from insulating threads. Several experiments are performed on the balls; and the following observations are made:

I. Ball A attracts B and A repels C.

II. Ball D attracts B and D has no effect on E.

III. A negatively charged rod attracts both A and E.

What are the charges, if any, on each ball?

C) + - + 0 0

3. Two uncharged conducting spheres, A and B, are suspended from insulating threads so that they touch each other. While a negatively charged rod is held near, but not touching sphere A, someone moves ball B away from A. How will the spheres be charged, if at all?

E)

Sphere A: +

Sphere B: -

4. Each of three objects has a net charge. Objects A and B attract one another. Objects B and C also attract one another, but objects A and C repel one another. Which one of the following table entries is a possible combination of the signs of the net charges on these three objects?

D)- + -

5. A conducting sphere has a net charge of -6.4 × 10-17 C. What is the approximate number of excess electrons on the sphere?

D) 400

6. Complete the following statement: When an ebonite rod is rubbed with animal fur, the rod becomes negatively charged as

D) negative charges are transferred from the fur to the rod.

7. Complete the following statement: When a glass rod is rubbed with silk cloth, the rod becomes positively charged as

B) negative charges are transferred from the rod to the silk.

8. A charged conductor is brought near an uncharged insulator. Which one of the following statements is true?

B) Both objects will attract each other.

9. An aluminum nail has an excess charge of +3.2 µC. How many electrons must be added to the nail to make it electrically neutral?

A) 2.0 × 10^13

10. Two uncharged, conducting spheres, A and B, are held at rest on insulating stands and are in contact. A positively charged rod is brought near sphere A as suggested in the figure. While the rod is in place, someone moves sphere B away from A. How will the spheres be charged, if at all?

C)

Sphere A: negative

Sphere B: positive

11. Consider three identical metal spheres, A, B, and C. Sphere A carries a charge of -2.0 µC; sphere B carries a charge of -6.0 µC; and sphere C carries a charge of +4.0 µC. Spheres A and B are touched together and then separated. Spheres B and C are then touched and separated. Does sphere C end up with an excess or a deficiency of electrons and how many electrons is it?

E) There is no excess or deficiency of electrons.

12. Two charged particles A and B are located near one another. Both the magnitude and direction of the force that particle A exerts on particle B is independent of

E) The magnitude and direction of the force are dependent on all of the above choices.

(the sign of charge B, the sign of charge A, the distance between A and B, the magnitude of the charge on B.)

13. Four point charges, each of the same magnitude, with varying signs are arranged at the corners of a square as shown. Which of the arrows labeled A, B, C, and D gives the correct direction of the net force that acts on the charge at the upper right corner?

B) B {there is a square pictured, it is the vector pointing SW from NE corner on the neg line}

14. Two positive point charges Q and 2Q are separated by a distance R. If the charge Q experiences a force of magnitude F when the separation is R, what is the magnitude of the force on the charge 2Q when the separation is 2R ?

A) F/4

15. A charge Q exerts a 1.2 N force on another charge q. If the distance between the charges is doubled, what is the magnitude of the force exerted on Q by q?

A) 0.30 N

16. At what separation will two charges, each of magnitude 6.0 mC, exert a force of 0.70 N on each other?

D) 0.68 m

17. One mole of a substance contains 6.02 × 1023 protons and an equal number of electrons. If the protons could somehow be separated from the electrons and placed in very small, individual containers separated by a million meters, what would be the magnitude of the electrostatic force exerted by one box on the other?

D) 8.4 × 10^7 N

18. Three charges are positioned as indicated in the figure. What are the horizontal and vertical components of the net force exerted on the +15 µC charge by the +11 µC and +13 µC charges?

E) horizontal: 76 N vertical: 370 N

19. A -4.0-µC charge is located 0.45 m to the left of a +6.0-µC charge. What is the magnitude and direction of the electrostatic force on the positive charge?

D) 1.1 N, to the left

20. Determine the ratio of the electrostatic force to the gravitational force between a proton and an electron, FE/FG. Note: k = 8.99 × 109 N-m2/C2; G = 6.672 × 10-11 N-m2/kg2; me = 9.109 × 10-31 kg; and mp = 1.672 × 10-27 kg.

D) 2.26 × 10^39

21. In Frame 1, two identical conducting spheres, A and B, carry equal amounts of excess charge that have the same sign. The spheres are separated by a distance d; and sphere A exerts an electrostatic force on sphere B that has a magnitude F. A third sphere, C, which is handled only by an insulating rod, is introduced in Frame 2. Sphere C is identical to A and B except that it is initially uncharged. Sphere C is touched first to sphere A, in Frame 2, and then to sphere B, in Frame 3, and is finally removed in Frame 4.

D) 3F/8

22. Three identical point charges, Q, are placed at the vertices of an equilateral triangle as shown in the figure. The length of each side of the triangle is d. Determine the magnitude and direction of the total electrostatic force on the charge at the top of the triangle.

A) , directed upward

23. Three charges are located along the x axis as shown in the drawing. The mass of the -1.2 µC is 4.0 × 10-9 kg. Determine the magnitude and direction of the acceleration of the -1.2 µC charge when it is allowed to move if the other two charges remain fixed.

B) 1 × 105 m/s2, to the left

24. Four point charges are held fixed at the corners of a square as shown in the figure. Which of the five arrows shown below most accurately shows the direction of the net force on the charge -Q due to the presence of the three other charges?

E) e

25. Is it possible to choose the value of Q (that is non-zero) such that the force on Q is zero? Explain why or why not.

Ans: E

26. Determine an expression for the magnitude and sign of Q so that the net force on the charge at A is zero newtons.

Ans: B

27. Which one of the following statements is true concerning the magnitude of the electric field at a point in space?

E) It is a measure of the electric force per unit charge on a test charge.

28. In the figure, point A is a distance L away from a point charge Q. Point B is a distance 4L away from Q. What is the ratio of the electric field at B to that at A, EB/EA?

A) 1/16

29. At which point (or points) is the electric field zero N/C for the two point charges shown on the x axis?

C) The electric field is zero somewhere on the x axis to the right of the -2q charge.

30. An electron traveling horizontally enters a region where a uniform electric field is directed upward. What is the direction of the force exerted on the electron once it has entered the field?

D) downward

31. Which one of the following statements is true concerning the strength of the electric field between two oppositely charged parallel plates?

E) It is constant between the plates except near the edges.

32. Two particles of the same mass carry charges +3Q and -2Q, respectively. They are shot into a region that contains a uniform electric field as shown. The particles have the same initial velocities in the positive x direction. The lines, numbered 1 through 5, indicate possible paths for the particles. If the electric field points in the negative y direction, what will be the resulting paths for these particles?

E) path 5 for +3Q and path 2 for -2Q

33. In which direction does the electric field point?

D) toward the bottom of the page

34. Which path would be followed by a helium atom (an electrically neutral particle)?

C) path 3

35. Which path would be followed by a charge +6Q?

E) path 5

36. What is the magnitude of the electric field due to a 6.0 × 10-9 C charge at a point located 0.025 m from the charge?

A) 8.6 × 102 N/C

37. Which one of the following statements concerning the direction of the electric field between the plates is true?

C) It points toward the negative plate.