OUT OF BOOK QUESTION. Sphere Y is now moved away from X, as in Figure (b).

Transcription

1 X and Y are two uncharged metal spheres on insulating stands, and are in contact with each other. A positively charged rod R is brought close to X as shown in Figure (a). Sphere Y is now moved away from X, as in Figure (b). What are the final charge states of X and Y? A) Both X and Y are neutral. B) X is positive and Y is neutral. C) X is neutral and Y is positive. D) X is negative and Y is positive. E) Both X and Y are negative. Answer: D

2 Page 715 Answer: Because they attract each other, they should have opposite charges. After they touch there are different cases may occur. 1) If + and equal then they will be neutral so afterward there will be no interaction between the spheres. 2) If + or are not the same amount then some less amount of change will be neutralized then the rest will be distributed between the spheres. Eventually they will have the same type of charges + or. After this happen, they will start to repel each other, they will not cling.

3 Two identical small charged spheres are a certain distance apart, and each one initially experiences an electrostatic force of magnitude F due to the other. With time, charge gradually leaks off of both spheres. When each of the spheres has lost half its initial charge, the magnitude of the electrostatic force will be A) 1/16 F. B) 1/8 F. C) 1/4 F. D) 1/2 F. Answer: C

4 When two point charges are a distance d part, the electric force that each one feels from the other has magnitude F. In order to make this force twice as strong, the distance would have to be changed to A) 2d. B) d. C) d/ 2 D) d/2. E) d/4. Answer: C

5 A point charge Q is located a short distance from a point charge 3Q, and no other charges are present. If the electrical force on Q is F, what is the electrical force on 3Q? A) F/3 B) F/ 3 C) 3 F D) 3F E) F Answer: E

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7 A positive point charge Q is fixed on a very large horizontal frictionless tabletop. A second positive point charge q is released from rest near the stationary charge and is free to move. Which statement best describes the motion of q after it is released? A) Its speed will be greatest just after it is released. B) Its acceleration is zero just after it is released. C) As it moves farther and farther from Q, its acceleration will keep increasing. D) As it moves farther and farther from Q, its speed will decrease. E) As it moves farther and farther from Q, its speed will keep increasing. Answer: E

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9 When two point charges are 2.0 cm apart, each one experiences a 1.0 N electric force due to the other charge. If they are moved to a new separation of 8.0 cm, the electric force on each of them is closest to A) 1.0 N. B) 4.0 N. C) 16 N. D) 0.25 N. E) N. Answer: E

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11 In the figure, charge q 1 = C is placed at the origin and charge q 2 = C is placed on the x axis, at x = 0.20 m. Where along the x axis can a third charge Q = 8.3 µc be placed such that the resultant force on this third charge is zero? Answer: 0.30 m

12 In the figure Q = 5.8 nc and all other quantities are accurate to 2 significant figures. What is the magnitude of the force on the charge Q? (k = 1/4πε 0 = N m 2 /C 2 ) A) N B) N C) N D) N Answer: A

13 A point charge is placed at each corner of a square with side length a. The charges all have the same magnitude q. Two of the charges are positive and two are negative, as shown in the figure. A fifth charge +q is placed at the center of the square. What is the direction and magnitude of the net electrostatic force on the fifth charge due to charges at the corners of the square? Note: Your answer for magnitude will be in terms of q, a, and some constants. For direction you may define x and y coordinates that you may define or use right/left/up/down words along with any angle if necessary.

14 Solution of Previous Question Mahmud

15 The figure shows two unequal point charges, q and Q, of opposite sign. Charge Q has greater magnitude than charge q. In which of the regions X, Y, Z will there be a point at which the net electric field due to these two charges is zero? A) only regions X and Z B) only region X C) only region Y D) only region Z E) all three regions Answer: B

16 Two point charges Q1 and Q2 of equal magnitudes and opposite signs are positioned as shown in the figure. Which of the arrows best represents the net electric field at point P due to these two charges? A) A B) B C) C D) D E) The field is equal to zero at point P. Answer: A

17 Three equal negative point charges are placed at three of the corners of a square of side d as shown in the figure. Which of the arrows represents the direction of the net electric field at the center of the square? A) A B) B C) C D) D E) The field is equal to zero at point P. Answer: C

18 A proton is placed in an electric field of intensity 700 N/C. What are the magnitude and direction of the acceleration of this proton due to this field? (m proton = kg, e = C) A) m/s 2 opposite to the electric field B) m/ s 2 opposite to the electric field C) m/s 2 in the direction of the electric field D) m/s 2 opposite to the electric field E) m/s 2 in the direction of the electric field Answer: C

19 In the figure, a ring 0.71 m in radius carries a charge of nc uniformly distributed over it. A point charge Q is placed at the center of the ring. The electric field is equal to zero at field point P, which is on the axis of the ring, and 0.73 m from its center. (ε 0 = C 2 /N m 2 ). The point charge Q should be A) 210 nc B) 300 nc C) 420 nc D) 210 nc E) 300 nc Answer: A

20 An electron is initially moving to the right when it enters a uniform electric field directed upwards. Which trajectory shown below will the electron follow? A) trajectory W B) trajectory X C) trajectory Y D) trajectory Z Answer: D

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22 Two large, flat, horizontally oriented plates both carrying +σ are parallel to each other, a distance d apart. What is the magnitude of electric field between the plates? A) σ/ε 0 B) σ/(ε 0 d) C) 0 D) 2σ/ε 0 E) 2σ/(ε 0 d) Answer: C

23 The figure shows three electric charges labeled Q1, Q2, Q3, and some electric field lines in the region surrounding the charges. What are the signs of the three charges? A) Q1 is positive, Q2 is negative, Q3 is positive. B) Q1 is negative, Q2 is positive, Q3 is negative. C) Q1 is positive, Q2 is positive, Q3 is negative. D) All three charges are negative. E) All three charges are positive. Answer: A

24 The figure below shows the electric field lines for two charged particles separated by a small distance. What are the signs of q1, q2 charges, and the ratio? A) q1 is positive, q2 is negative, and q1/q2= 3. B) q1 is negative, q2 is positive, and q1/q2= 3. C) q1 is positive, q2 is negative, and q1/q2= 1/3. D) q1 is negative, q2 is positive, and q1/q2= 1/3. E) Both charges are positive, and q1/q2=1. Answer: D

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