Discussed In Chapter 1:Electrostatics

Q1) Which is stronger, the gravitational force between a proton and an electron or the electrical force? 1 2 3 1) the gravitational force by a factor of 1015 2) the gravitational force by a factor of 1039 3) the electrical force by a factor of 1015 4) the electrical force by a factor of 1039 5) none of the above

Q2) 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 charges on these three objects?

A B C 1) + + - 2) - + + 3) + - - 4) - + - 5) - - +

Q3) Strictly speaking, will a penny be slightly more massive if it has a negative charge or a positive charge?

1) negative charge 2) positive charge 3) it has the same mass either way Q4) You comb your hair and the comb becomes negatively charged. Strictly speaking, how will the mass of your hair change?

1) it will increase 2) it will decrease 3) it will not change

Q5) A positively charged object is placed close to a conducting object attached to an insulating glass pedestal (a). After the opposite side of the conductor is grounded for a short time interval (b), the conductor becomes negatively charged (c). Based on this information, we can conclude that within the conductor

1) both positive and negative charges move freely. 2) only negative charges move freely. 3) only positive charges move freely. 4) We can’t really conclude anything.

Q6) (a) A charged rod is brought near a suspended object, which is attracted by the rod. Can we conclude that the suspended object is charged? (b) What if the suspended object is repelled by the rod?

1) (a) yes (b) yes 2) (a) yes (b) no 3) (a) no (b) no 4) (a) no (b) yes Q7) Complete the following statement: When a plastic rod is rubbed with animal fur, the rod becomes negatively charged as

1) protons are transferred from the fur to the rod. 2) electrons are transferred from the rod to the fur. 3) electrons are created on the surface of the rod. 4) electrons are transferred from the fur to the rod. 5) protons are transferred from the rod to the fur.

Q8) Complete the following statement: When a glass rod is rubbed with silk cloth, the rod becomes positively charged as

1) positive charges are transferred from the silk to the rod. 2) negative charges are transferred from the rod to the silk. 3) positive charges are created on the surface of the rod. 4) negative charges are transferred from the silk to the rod. 5) positive charges are transferred from the rod to the silk.

Q9) Which one of the following statements best explains why tiny bits of paper are attracted to a charged rubber rod?

1) Paper is naturally a positive material. 2) Paper is naturally a negative material. 3) The paper becomes polarized by induction. 4) Rubber and paper always attract each other. 5) The paper acquires a net positive charge by induction. Q10) A neutral metal ball is suspended by a string. A positively charged insulating rod is placed near the ball, which is observed to be attracted to the rod. This is because:

1) the ball becomes positively charged by induction 2) the ball becomes negatively charged by induction 3) the number of electrons in the ball is more than the number in the rod 4) the string is not a perfect insulator 5) there is a rearrangement of the electrons in the ball

Q11) Three pithballs are suspended from thin threads. Various objects are then rubbed against other objects (nylon against silk, glass against polyester, etc.) and each of the pithballs is charged by touching them with one of these objects. It is found that pithballs 1 and 2 repel each other and that pithballs 2 and 3 repel each other. From this we can conclude that

1) 1 and 3 carry charges of opposite sign. 2) 1 and 3 carry charges of equal sign. 3) all three carry the charges of the same sign. 4) one of the objects carries no charge. 5) we need to do more experiments to determine the sign of the charges. Q12) A positively charged insulating rod is brought close to an object that is suspended by a string. If the object is attracted toward the rod we can conclude:

1) the object is positively charged 2) the object is negatively charged 3) the object is an insulator 4) the object is a conductor 5) none of the above

Q13) A thin stream of water bends toward a negatively charged rod. When a positively charged rod is placed near the stream, it will bend in the

1) opposite direction 2) same direction 3) it will not bend at all

Q14) Two protons are near each other. Each feels an electrostatic repulsion of magnitude Felec and a gravitational attraction of magnitude Fgrav, due to the other charge. As the charges are moved F apart, the ratio elec Fgrav

1) increases 2) decreases 3) remains constant Q15) A hydrogen atom is composed of a nucleus containing a single proton, about which a single electron orbits. The electric force between the two particles is 2.3 1039 greater than the gravitational force! If we can adjust the distance between the two particles, can we find a separation at which the electric and gravitational forces are equal?

1) Yes, we must move the particles farther apart. 2) Yes, we must move the particles closer together. 3) no, at any distance

Q16) Two uniformly charged spheres are firmly fastened to a table. The charge on sphere 2 is three times the charge on sphere 1. Which force diagram correctly shows the magnitude and direction of the electrostatic forces:

Q17) Particle A and particle B interact with each other. Particle A has twice the charge of particle B. Compared to the force on particle A, the force on particle B is

1) four times as much 2) twice as much 3) the same 4) half as much 5) one-fourth as much Q18) Two charged particles held close to each other are released. As they move, the force on each particle increases. Therefore, the particles have

1) the same sign 2) opposite signs 3) not enough information given

Q19) Two charged particles repel each other with a force F. If the charge of one of the particles is doubled and the distance between them is also doubled, then the force will be

1) F 2) 2 F 3) F / 2 4) F / 4 5) none of the above

Q20) Two charges attract each other with a force of 1.50 N. What will be the force if the distance between them is reduced to one- ninth of its original value?

1) 0.0185 N 2) 0.167 N 3) 13.5 N 4) 122 N 5) none of the above Q21) The figure below shows four situations in which charged particles are fixed in place on an axis. In which situation(s) is there a point to the left of the particles where an electron will be in equilibrium? 1) a and b 2) a and c 3) b and d 4) c and d 5) none of the above

Q22) Four point charges have equal magnitudes. Three are positive and one is negative, as the drawing shows. They are fixed in place on the same straight line, and adjacent charges are equally separated by a distance d. On which charge is the magnitude of the net force the strongest?

1) A 2) B 3) C 4) D

Q23) Consider three charges, as shown below. Rank the magnitude of the forces on each charge from smallest to largest.

1) F2 < F1 = F3

2) F1 < F2 < F3 3) F3 < F2 < F1

4) F2 < F1 = F3 Q24) 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?

1) A 2) B 3) C 4) D 5) the net force on that charge is zero

Q25) The figure shows three small spheres that have charges of equal magnitudes and rest on a frictionless surface. Spheres y and z are fixed in place and are equally distance from sphere x. If sphere x is released from rest, which of the five paths shown will it take? 1) A 2) B 3) C 4) D 5) E Q26) The figure here shows three arrangements of an electron e and two protons p. (a) In which of the 3 arrangements is the magnitude of the net electrostatic force on the electron the greatest? (b) In situation c, is the angle between the net force on the electron and the line labeled d less than or more than 45°?

1) (a) a (b) greater than 2) (a) b (b) greater than 3) (a) c (b) greater than 4) (a) a (b) less than 5) (a) c (b) less than

Q27) Two charges with magnitude Q experience a force F when held a distance r apart. What is the force between two charges of magnitude 2Q held a distance r/2 apart?

1) F/4 2) F/2 3) F 4) 4F 5) 16F Q28) Two particles, each with charge Q, and a third particle, with charge q, are placed at the vertices of an equilateral triangle as shown. The total force on the particle with charge q is:

1) parallel to the left side of the triangle 2) parallel to the right side of the triangle 3) parallel to the bottom side of the triangle 4) perpendicular to the bottom side of the triangle 5) perpendicular to the left side of the triangle

Q29) An electron and a proton are separated by a distance d and then are released from rest. When they collide, the distance from the electron’s original position will be ______.

1) > d/2 2) = d/2 3) < d/2 4) impossible to tell.

Q30) An aluminum nail has an excess charge of +3.2 C. How many electrons must be added to the nail to make it electrically neutral?

1) 2.0  1013 2) 2.0  1019 3) 3.2  10-6 4) 3.2  106 5) 5.0  10-14 Q31) Initially, sphere A has a charge of -50e and sphere B has a charge of +20e. The spheres are made of conducting material and are identical in size. If the spheres then touch, what is the resulting charge on sphere A?

1) –30 e 2) –15 e 3) 0 4) 30 e 5) none of the above

Q32) 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 +5.0 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?

1) deficiency, 6 × 1013 2) excess, 2 × 1013 3) excess, 3 × 1013 4) deficiency, 3 × 1012 5) deficiency, 1 × 1012