Chapter 21, PHY: Chap 22, Chap 23

. An electroscope is charged by induction using a glass rod that has been made positive by rubbing it with silk. The electroscope leaves: A. gain electrons B. gain protons C. lose electrons D. lose protons E. gain an equal number of protons and electrons

A

31. A 5.0-C charge is 10 m from a −2.0-C charge. The electrostatic force on the positive charge is: A. 9.0 × 108 N toward the negative charge B. 9.0 × 108 N away from the negative charge C. 9.0 × 109 N toward the negative charge D. 9.0 × 109 N away from the negative charge

A

A 30-N/C uniform electric field points perpendicularly toward the left face of a large neutral conducting sheet. The surface charge density in C/m 2 on the left and right faces, respectively, are: A. −2.7 × 10−9 C/m 2 ; +2.7 × 10−9 C/m 2 B. +2.7 × 10−9 C/m 2 ; −2.7 × 10−9 C/m 2 C. −5.3 × 10−9 C/m 2 ; +5.3 × 10−9 C/m 2 D. +5.3 × 10−9 C/m 2 ; −5.3 × 10−9 C/m 2 E. 0; 0

A

A charged particle is placed in an electric field that varies with location. No force is exerted on this charge: A. at locations where the electric field is zero B. at locations where the electric field strength is 1/(1.6 × 10^−19)N/C C. if the particle is moving along a field line D. if the particle is moving perpendicularly to a field line E. if the field is caused by an equal amount of positive and negative charge

A

A positively charged insulating rod is brought close to an object that is suspended by a string. If the object is repelled away from the rod we can conclude: A. the object is positively charged B. the object is negatively charged C. the object is an insulator D. the object is a conductor E. none of the above

A

A positively charged metal sphere A is brought into contact with an uncharged metal sphere B. As a result: A. both spheres are positively charged B. A is positively charged and B is neutral C. A is positively charged and B is negatively charged D. A is neutral and B is positively charged E. A is neutral and B is negatively charged

A

Charge Q is distributed uniformly throughout a spherical insulating shell. The net electric flux in N · m2 /C through the inner surface of the shell is: A. 0 B. Q/60 C. 2Q/60 D. Q/4π60 E. Q/2π60 ans: A

A

Charge is distributed on the surface of a spherical conducting shell. A point particle with charge q is inside. If polarization effects are negligible the electrical force on the particle is greatest when: A. it is near the inside surface of the balloon B. it is at the center of the balloon C. it is halfway between the balloon center and the inside surface D. it is anywhere inside (the force is same everywhere and is not zero) E. it is anywhere inside (the force is zero everywhere)

A

Experimenter A uses a test charge q0 and experimenter B uses a test charge −2q0 to measure an electric field produced by stationary charges. A finds a field that is: A. the same in both magnitude and direction as the field found by B B. greater in magnitude than the field found by B C. less in magnitude than the field found by B D. opposite in direction to the field found by B E. either greater or less than the field found by B, depending on the accelerations of the test charges

A

The charge on a glass rod that has been rubbed with silk is called positive: A. by arbitrary convention B. so that the proton charge will be positive C. to conform to the conventions adopted for G and m in Newton's law of gravitation D. because like charges repel E. because glass is an insulator

A

The magnitude of the force of a 400-N/C electric field on a 0.02-C point charge is: A. 8.0N B. 8 × 10^−5 N C. 8 × 10^−3 N D. 0.08N E. 2 × 1011 N

A

The units of the electric field are: A. J/(C·m) B. J/C C. J·C D. J/m E. none of these

A

Two particles A and B have identical charge Q. For a net force of zero to be exerted on a third charged particle it must be placed: A. midway between A and B B. on the perpendicular bisector of the line joining A and B but away from the line C. on the line joining A and B, not between the particles D. on the line joining A and B, closer to one of them than the other E. at none of these places (there is no place)

A

Two point particles, with the same charge, are located at two vertices of an equilateral triangle. A third charged particle is placed so the electric field at the third vertex is zero. The third particle must: A. be on the perpendicular bisector of the line joining the first two charges B. be on the line joining the first two charges C. have the same charge as the first two particles D. have charge of the same magnitude as the first two charges but its charge may have a different sign E. be at the center of the triangle

A

Two thin spherical shells, one with radius R and the other with radius 2R, surround an isolated charged point particle. The ratio of the number of field lines through the larger sphere to the number through the smaller is: A. 1 B. 2 C. 4 D. 1/2 E. 1/4

A

24. Consider the following procedural steps: 1. ground an electroscope 2. remove the ground from the electroscope 3. touch a charged rod to the electroscope 4. bring a charged rod near, but not touching, the electroscope 5. remove the charged rod To charge an electroscope by induction, use the sequence: A. 1, 4, 5, 2 B. 4, 1, 2, 5 C. 3, 1, 2, 5 D. 4, 1, 5, 2 E. 3, 5

B

A long line of charge with λf charge per unit length runs along the cylindrical axis of a cylindrical shell which carries a charge per unit length of λc. The charge per unit length on the inner and outer surfaces of the shell, respectively are: A. λf and λc B. −λf and λc + λf C. −λf and λc − λc D. λf + λc and λc − λf E. λf − λc and λc + λf

B

A particle with a charge of 5 × 10−6 C and a mass of 20 g moves uniformly with a speed of 7 m/s in a circular orbit around a stationary particle with a charge of −5×10−6 C. The radius of the orbit is: A. 0 B. 0.23 m C. 0.62 m D. 1.6 E. 4.4 m

B

An electric dipole consists of a particle with a charge of +6×10^−6 C at the origin and a particle with a charge of −6 × 10^−6 Conthe x axis at x =3 × 10^−3 m. Its dipole moment is: A. 1.8 × 10^−8 C · m, in the positive x direction B. 1.8 × 10^−8 C · m, in the negative x direction C. 0 because the net charge is 0 D. 1.8 × 10^−8 C · m, in the positive y direction E. 1.8 × 10^−8 C · m, in the negative y direction

B

An electrical insulator is a material: A. containing no electrons B. through which electrons do not flow easily C. that has more electrons than protons on its surface D. cannot be a pure chemical element E. must be a crysta

B

An electron traveling north enters a region where the electric field is uniform and points north. The electron: A. speeds up B. slows down C. veers east D. veers west E. continues with the same speed in the same direction

B

Charge Q is distributed uniformly throughout a spherical insulating shell. The net electric flux in N · m2 /C through the outer surface of the shell is: A. 0 B. Q/60 C. 2Q/60 D. Q/460 E. Q/2π60

B

Choose the correct statement concerning electric field lines: A. field lines may cross B. field lines are close together where the field is large C. field lines point away from a negatively charged particle D. a charged point particle released from rest moves along a field line E. none of these are correct

B

Particles 1, with charge q1, and 2, with charge q2, are on the x axis, with particle 1 at x = a and particle 2 at x = −2a. For the net force on a third charged particle, at the origin, to be zero, q1 and q2 must be related by q2 =: A. 2q1 B. 4q1 C. −2q1 D. −4q1 E. −q1/4

B

4. The total negative charge on the electrons in 1 mol of helium (atomic number 2, molar mass 4) is: A. 4.8 × 104 C B. 9.6 × 104 C C. 1.9 × 105 C D. 3.8 × 105 C E. 7.7 × 105 C

C

A 3.5-cm radius hemisphere contains a total charge of 6.6 × 10−7 C. The flux through the rounded portion of the surface is 9.8 × 104 N · m2 /C. The flux through the flat base is: A. 0 B. +2.3 × 104 N · m2 /C C. −2.3 × 104 N · m2 /C D. −9.8 × 104 N · m2 /C E. +9.8 × 104 N · m2 /C

C

A conducting sphere of radius 0.01 m has a charge of 1.0 × 10−9 C deposited on it. The magnitude of the electric field in N/C just outside the surface of the sphere is: A. 0 B. 450 C. 900 D. 4500 E. 90, 000

C

A conductor is distinguished from an insulator with the same number of atoms by the number of: A. nearly free atoms B. electrons C. nearly free electrons D. protons E. molecules

C

A hollow conductor is positively charged. A small uncharged metal ball is lowered by a silk thread through a small opening in the top of the conductor and allowed to touch its inner surface. After the ball is removed, it will have: A. a positive charge B. a negative charge C. no appreciable charge D. a charge whose sign depends on what part of the inner surface it touched E. a charge whose sign depends on where the small hole is located in the conductor

C

A particle with charge 2-µC is placed at the origin, an identical particle, with the same charge, is placed 2 m from the origin on the x axis, and a third identical particle, with the same charge, is placed 2 m from the origin on the y axis. The magnitude of the force on the particle at the origin is: A. 9.0 × 10−3 N B. 6.4 × 10−3 N C. 1.3 × 10−2 N D. 1.8 × 10−2 N E. 3.6 × 10−2 N

C

A particle with charge Q is placed outside a large neutral conducting sheet. At any point in the interior of the sheet the electric field produced by charges on the surface is directed: A. toward the surface B. away from the surface C. toward Q D. away from Q E. none of the above

C

A round wastepaper basket with a 0.15-m radius opening is in a uniform electric field of 300 N/C, perpendicular to the opening. The total flux through the sides and bottom, in N · m2 C, is: A. 0 B. 4.2 C. 21 D. 280 E. can not tell without knowing the areas of the sides and bottom

C

A small object has charge Q. Charge q is removed from it and placed on a second small object. The two objects are placed 1 m apart. For the force that each object exerts on the other to be a maximum. q should be: A. 2Q B. Q C. Q/2 D. Q/4 E. 0

C

An electron traveling north enters a region where the electric field is uniform and points west. The electron: A. speeds up B. slows down C. veers east D. veers west E. continues with the same speed in the same direction

C

An isolated charged point particle produces an electric field with magnitude E at a point 2m away. At a point 1m from the particle the magnitude of the field is: A. E B. 2E C. 4E D. E/2 E. E/4

C

Charge is distributed uniformly on the surface of a large flat plate. The electric field 2 cm from the plate is 30 N/C. The electric field 4 cm from the plate is: A. 120 N/C B. 80 N/C C. 30 N/C D. 15 N/C E. 7.5 N/C

C

Consider Gauss's law: En · dAn = q/60. Which of the following is true? A. En must be the electric field due to the enclosed charge B. If q = 0, then En = 0 everywhere on the Gaussian surface C. If the three particles inside have charges of +q, +q, and −2q, then the integral is zero D. on the surface En is everywhere parallel to dAn E. If a charge is placed outside the surface, then it cannot affect En at any point on the surface

C

Positive charge Q is distributed uniformly throughout an insulating sphere of radius R, centered at the origin. A particle with positive charge Q is placed at x = 2R on the x axis. The magnitude of the electric field at x = R/2 on the x axis is: A. Q/4π60R2 B. Q/8π60R2 C. Q/72π60R2 D. 17Q/72π60R2 E. none of these

C

The leaves of a positively charged electroscope diverge more when an object is brought near the knob of the electroscope. The object must be: A. a conductor B. an insulator C. positively charged D. negatively charged E. uncharged

C

The total negative charge on the electrons in 1 kg of helium (atomic number 2, molar mass 4) is: A. 48 C B. 2.4 × 107 C C. 4.8 × 107 C D. 9.6 × 108 C E. 1.9 × 108 C

C

To make an uncharged object have a negative charge we must: A. add some atoms B. remove some atoms C. add some electrons D. remove some electrons E. write down a negative sign

C

Two identical charges, 2.0 m apart, exert forces of magnitude 4.0 N on each other. The value of either charge is: A. 1.8 × 10−9 C B. 2.1 × 10−5 C C. 4.2 × 10−5 C D. 1.9 × 105 C E. 3.8 × 105 C

C

Two identical conducting spheres A and B carry equal charge. They are separated by a distance much larger than their diameters. A third identical conducting sphere C is uncharged. Sphere C is first touched to A, then to B, and finally removed. As a result, the electrostatic force between A and B, which was originally F, becomes: A. F/2 B. F/4 C. 3F/8 D. F/16 E. 0

C

Two large insulating parallel plates carry charge of equal magnitude, one positive and the other negative, that is distributed uniformly over their inner surfaces. Rank the points 1 through 5 according to the magnitude of the electric field at the points, least to greatest. 1 23 4 5 A. 1, 2, 3, 4, 5 B. 2, then 1, 3, and 4 tied, then 5 C. 1, 4, and 5 tie, then 2 and 3 tie D. 2 and 3 tie, then 1 and 4 tie, then 5 E. 2 and 3 tie, then 1, 4, and 5 tie

C

Two point particles, with a charges of q1 and q2, are placed a distance r apart. The electric field is zero at a point P between the particles on the line segment connecting them. We conclude that: A. q1 and q2 must have the same magnitude and sign B. P must be midway between the particles C. q1 and q2 must have the same sign but may have different magnitudes D. q1 and q2 must have equal magnitudes and opposite signs E. q1 and q2 must have opposite signs and may have different magnitudes

C

10 C of charge are placed on a spherical conducting shell. A particle with a charge of −3 C is placed at the center of the cavity. The net charge on the inner surface of the shell is: A. −7 C B. −3 C C. 0 C D. +3 C E. +7 C

D

A 200-N/C electric field is in the positive x direction. The force on an electron in this field is: A. 200N in the positive x direction B. 200N in the negative x direction C. 3.2 × 10^−17 N in the positive x direction D. 3.2 × 10^−17 N in the negative x direction E. 0

D

A charged insulator can be discharged by passing it just above a flame. This is because the flame: A. warms it B. dries it C. contains carbon dioxide D. contains ions E. contains more rapidly moving atoms

D

A charged point particle is placed at the center of a spherical Gaussian surface. The electric flux ΦE is changed if: A. the sphere is replaced by a cube of the same volume B. the sphere is replaced by a cube of one-tenth the volume C. the point charge is moved off center (but still inside the original sphere) D. the point charge is moved to just outside the sphere E. a second point charge is placed just outside the sphere

D

A coulomb is the same as: A. an ampere/second B. half an ampere·second2 C. an ampere/meter2 D. an ampere·second E. a newton·meter2

D

A cylinder has a radius of 2.1 cm and a length of 8.8 cm. Total charge 6.1×10−7 C is distributed uniformly throughout. The volume charge density is: A. 5.3 × 10−5 C/m3 B. 5.3 × 10−5 C/m2 C. 8.5 × 10−4 C/m3 D. 5.0 × 10−3 C/m3 E. 6.3 × 10−2 C/m3

D

A kiloampere·hour is a unit of: A. current B. charge per time C. power D. charge E. energy

D

A physics instructor in an anteroom charges an electrostatic generator to 25 µC, then carries it into the lecture hall. The net electric flux in N · m2/C through the lecture hall walls is: A. 0 B. 25 × 10−6 C. 2.2 × 105 D. 2.8 × 106 E. can not tell unless the lecture hall dimensions are given

D

A point particle with charge q is at the center of a Gaussian surface in the form of a cube. The electric flux through any one face of the cube is: A. q/60 B. q/4π60 C. q/360 D. q/660 E. q/1260

D

A spherical conducting shell has charge Q. A particle with charge q is placed at the center of the cavity. The charge on the inner surface of the shell and the charge on the outer surface of the shell, respectively, are: A. 0, Q B. q, Q − q C. Q, 0 D. −q, Q + q E. −q, 0

D

An electric field is most directly related to: A. the momentum of a test charge B. the kinetic energy of a test charge C. the potential energy of a test charge D. the force acting on a test charge E. the charge carried by a test charge

D

An isolated charged point particle produces an electric field with magnitude E at a point 2m away from the charge. A point at which the field magnitude is E/4 is: A. 1m away from the particle B. 0.5m away from the particle C. 2m away from the particle D. 4m away from the particle E. 8m away from the particle

D

Charge Q is distributed uniformly throughout an insulating sphere of radius R. The magnitude of the electric field at a point R/2 from the center is: A. Q/4π60R2 B. Q/π60R2 C. 3Q/4π60R2 D. Q/8π60R2 E. none of these

D

Charge Q is spread uniformly along the circumference of a circle of radius R. A point particle with charge q is placed at the center of this circle. The total force exerted on the particle can be calculated by Coulomb's law: A. just use R for the distance B. just use 2R for the distance C. just use 2πR for the distance D. the result of the calculation is zero E. none of the abov

D

Charge is distributed uniformly along a long straight wire. The electric field 2 cm from the wire is 20 N/C. The electric field 4 cm from the wire is: A. 120 N/C B. 80 N/C C. 40 N/C D. 10 N/C E. 5 N/C

D

Charge is placed on the surface of a 2.7-cm radius isolated conducting sphere. The surface charge density is uniform and has the value 6.9 × 10−6 C/m 2 . The total charge on the sphere is: A. 5.6 × 10−10 C B. 2.1 × 10−8 C C. 4.7 × 10−8 C D. 6.3 × 10−8 C E. 9.5 × 10−3 C

D

Let k denote 1/4π60. The magnitude of the electric field at a distance r from an isolated point particle with charge q is: A. kq/r B. kr/q C. kq/r^3 D. kq/r^2 E. kq^2/r^2

D

Positive charge Q is placed on a conducting spherical shell with inner radius R1 and outer radius R2. A point charge q is placed at the center of the cavity. The magnitude of the electric field at a point outside the shell, a distance r from the center, is: A. zero B. Q/4π60r2 C. q/4π60r2 D. (q + Q)/4π60r2 E. (q + Q)/4π60(R21 − r2)

D

Positive charge Q is placed on a conducting spherical shell with inner radius R1 and outer radius R2. A point charge q is placed at the center of the cavity. The magnitude of the electric field produced by the charge on the inner surface at a point in the interior of the conductor, a distance r from the center, is: A. 0 B. Q/4vπ60R21 C. Q/4π60R22 D. q/4π60r2 E. Q/4π60r

D

The electric field at a distance of 10 cm from an isolated point particle with a charge of 2×10^−9 C is: A. 1.8N/C B. 180N/C C. 18N/C D. 1800N/C E. none of these

D

The electric field due to a uniform distribution of charge on a spherical shell is zero: A. everywhere B. nowhere C. only at the center of the shell D. only inside the shell E. only outside the shell

D

The flux of the electric field (24 N/C)ˆi + (30 N/C)ˆj + (16 N/C) ˆ k through a 2.0 m2 portion of the yz plane is: A. 32 N · m2 /C B. 34 N · m2 /C C. 42 N · m2 /C D. 48 N · m2 /C E. 60 N · m2 /C

D

The magnitude of the charge on an electron is approximately: A. 1023 C B. 10−23 C C. 1019 C D. 10−19 C E. 109 C

D

The outer surface of the cardboard center of a paper towel roll: A. is a possible Gaussian surface B. cannot be a Gaussian surface because it encloses no charge C. cannot be a Gaussian surface since it is an insulator D. cannot be a Gaussian surface because it is not a closed surface E. none of the above

D

The units of 1/4π60 are: A. N2C2 B. N · m/C C. N2 · m2/C2 D. N · m2/C2 E. m2/C2

D

The units of the electric field are: A. N · C^2 B. C/N C. N D. N/C E. C/m^2

D

To make an uncharged object have a positive charge: A. remove some neutrons B. add some neutrons C. add some electrons D. remove some electrons E. heat it to cause a change of phase

D

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: A. parallel to the left side of the triangle B. parallel to the right side of the triangle C. parallel to the bottom side of the triangle D. perpendicular to the bottom side of the triangle E. perpendicular to the left side of the triangle

D

Two uncharged metal spheres, L and M, are in contact. A negatively charged rod is brought close to L, but not touching it, as shown. The two spheres are slightly separated and the rod is then withdrawn. As a result: insulating supports A. both spheres are neutral B. both spheres are positive C. both spheres are negative D. L is negative and M is positive E. L is positive and M is negative

D

When a hard rubber rod is given a negative charge by rubbing it with wool: A. positive charges are transferred from rod to wool B. negative charges are transferred from rod to wool C. positive charges are transferred from wool to rod D. negative charges are transferred from wool to rod E. negative charges are created and stored on the rod

D

When a piece of paper is held with one face perpendicular to a uniform electric field the flux through it is 25 N · m2 /C. When the paper is turned 25◦ with respect to the field the flux through it is: A. 0 B. 12 N · m2/C C. 21 N · m2/C D. 23 N · m2/C E. 25 N · m2/C

D

. The table below gives the electric flux in N · m2/C through the ends and round surfaces of four Gaussian surfaces in the form of cylinders. Rank the cylinders according to the charge inside, from the most negative to the most positive. left end right end rounded surface cylinder 1: +2 × 10−9 +4 × 10−9 −6 × 10−9 cylinder 2: +3 × 10−9 −2 × 10−9 +6 × 10−9 cylinder 3: −2 × 10−9 −5 × 10−9 +3 × 10−9 cylinder 4: +2 × 10−9 −5 × 10−9 −3 × 10−9 A. 1, 2, 3, 4 B. 4, 3, 2, 1 C. 3, 4, 2, 1 D. 3, 1, 4, 2 E. 4, 3, 1, 2

E

10 C of charge are placed on a spherical conducting shell. A particle with a charge of −3 C is placed at the center of the cavity. The net charge on the outer surface of the shell is: A. −7 C B. −3 C C. 0 C D. +3 C E. +7 C

E

A certain physics textbook shows a region of space in which two electric field lines cross each other. We conclude that: A. at least two point charges are present B. an electrical conductor is present C. an insulator is present D. the field points in two directions at the same place E. the author made a mistake

E

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: A. the ball becomes positively charged by induction B. the ball becomes negatively charged by induction C. the number of electrons in the ball is more than the number in the rod D. the string is not a perfect insulator E. there is a rearrangement of the electrons in the bal

E

A particle with charge 5.0-µC is placed at the corner of a cube. The total electric flux in N · m2 /C through all sides of the cube is: A. 0 B. 7.1 × 104 C. 9.4 × 104 D. 1.4 × 105 E. 5.6 × 105

E

A particle with charge Q is on the y axis a distance a from the origin and a particle with charge q is on the x axis a distance d from the origin. The value of d for which the x component of the force on the second particle is the greatest is: A. 0 B. a C. √2a D. a/2 E. a/√2

E

A point particle with charge q is placed inside the cube but not at its center. The electric flux through any one side of the cube: A. is zero B. is q/60 C. is q/460 D. is q/660 E. cannot be computed using Gauss' law

E

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: A. the object is positively charged B. the object is negatively charged C. the object is an insulator D. the object is a conductor E. none of the above

E

A total charge of 6.3×10−8 C is distributed uniformly throughout a 2.7-cm radius sphere. The volume charge density is: A. 3.7 × 10−7 C/m 3 B. 6.9 × 10−6 C/m 3 C. 6.9 × 10−6 C/m 2 D. 2.5 × 10−4 C/m 3 E. 7.6 × 10−4 C/m

E

A wire carries a steady current of 2A. The charge that passes a cross section in 2s is: A. 3.2×10−19 C B. 6.4×10−19 C C. 1C D. 2C E. 4C

E

A wire contains a steady current of 2 A. The number of electrons that pass a cross section in 2 s is: A. 2 B. 4 C. 6.3 × 1018 D. 1.3 × 1019 E. 2.5 × 1019

E

As used in the definition of electric field, a "test charge": A. has zero charge B. has charge of magnitude 1C C. has charge of magnitude 1.6 × 10−19 C D. must be an electron E. none of the above

E

Charge is distributed uniformly on the surface of a spherical balloon (an insulator). A point particle with charge q is inside. The electrical force on the particle is greatest when: A. it is near the inside surface of the balloon B. it is at the center of the balloon C. it is halfway between the balloon center and the inside surface D. it is anywhere inside (the force is same everywhere and is not zero) E. it is anywhere inside (the force is zero everywhere)

E

Choose the INCORRECT statement: A. Gauss' law can be derived from Coulomb's law B. Gauss' law states that the net number of lines crossing any closed surface in an outward direction is proportional to the net charge enclosed within the surface C. Coulomb's law can be derived from Gauss' law and symmetry D. Gauss' law applies to a closed surface of any shape E. According to Gauss' law, if a closed surface encloses no charge, then the electric field must vanish everywhere on the surface

E

Electric field lines: A. are trajectories of a test charge B. are vectors in the direction of the electric field C. form closed loops D. cross each other in the region between two point charges E. are none of the above

E

The force exerted by a uniform electric field on a dipole is: A. parallel to the dipole moment B. perpendicular to the dipole moment C. parallel to the electric field D. perpendicular to the electric field E. none of the above

E

Two charged point particles are located at two vertices of an equilateral triangle and the electric field is zero at the third vertex. We conclude: A. the two particles have charges with opposite signs and the same magnitude B. the two particles have charges with opposite signs and different magnitudes C. the two particles have identical charges D. the two particles have charges with the same sign but different magnitudes E. at least one other charged particle is present

E

Two particles have charges Q and −Q (equal magnitude and opposite sign). For a net force of zero to be exerted on a third charge it must be placed: A. midway between Q and −Q B. on the perpendicular bisector of the line joining Q and −Q, but not on that line itself C. on the line joining Q and −Q, to the side of Q opposite −Q D. on the line joining Q and −Q, to the side of −Q opposite Q E. at none of these places (there is no place)

E

Two point particles, one with charge +8 × 10^−9 C and the other with charge −2 × 10^−9 C, are separated by 4m. The electric field in N/C midway between them is: A. 9 × 109 B. 13, 500 C. 135, 000 D. 36 × 10^−9 E. 22.5

E

A spherical shell has an inner radius of 3.7 cm and an outer radius of 4.5 cm. If charge is distributed uniformly throughout the shell with a volume density of 6.1 × 10−4 C/m 3 the total charge is: A. 1.0 × 10−7 C B. 1.3 × 10−7 C C. 2.0 × 10−7 C D. 2.3 × 10−7 C E. 4.0 × 10−7 C

a

A negatively charged rubber rod is brought near the knob of a positively charged electroscope. The result is that: A. the electroscope leaves will move farther apart B. the rod will lose its charge C. the electroscope leaves will tend to collapse D. the electroscope will become discharged E. nothing noticeable will happen

c

Two small charged objects attract each other with a force F when separated by a distance d. If the charge on each object is reduced to one-fourth of its original value and the distance between them is reduced to d/2 the force becomes: A. F/16 B. F/8 C. F/4 D. F/2 E. F

c

In the Rutherford model of the hydrogen atom, a proton (mass M, charge Q) is the nucleus and an electron (mass m, charge q) moves around the proton in a circle of radius r. Let k denote the Coulomb force constant (1/4π60) and G the universal gravitational constant. The ratio of the electrostatic force to the gravitational force between electron and proton is: A. kQq/GMmr2 B. GQq/kMm C. kMm/GQq D. GMm/kQq E. kQq/GMm

e

Two particles, X and Y, are 4 m apart. X has a charge of 2Q and Y has a charge of Q. The force of X on Y: A. has twice the magnitude of the force of Y on X B. has half the magnitude of the force of Y on X C. has four times the magnitude of the force of Y on X D. has one-fourth the magnitude of the force of Y on X E. has the same magnitude as the force of Y on X

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