Deck 21: Electric Charge

Question 1

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

Answer 1

has the same magnitude as the force of Y on X

Question 2

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

Answer 2

add some electrons

Question 3

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

Answer 3

Q/2

Question 4

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

Question 5

A negatively charged rubber rod is brought near the knob of a positively charged electroscope. The result is that:

A) electroscope leaves will move farther apart
B) the rod will lose its charge
C) electroscope leaves will tend to collapse
D) electroscope will become discharged
E) nothing noticeable will happen

Question 6

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

Question 7

The diagram shows two pairs of highly charged plastic cubes. Cubes 1 and 2 attract each and cubes 1 and 3 repel each other. Which of the following illustrates the forces of cube 2 on 3 and cube 3 on 2?

A) I
B) II
C) III
D) IV
E) V

Question 8

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

Question 9

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

Question 10

An electrical insulator is a material:

A) containing no electrons
B) through which electrons do not flow easily
C) which has more electrons than protons on its surface
D) cannot be a pure chemical element
E) must be a crystal

Question 11

The units of 1/4 $\pi$$\varepsilon$ ₀ are:

A) N²/C²
B) N.m/C
C) N².m²/C²
D) N.m²/C²
E) m²/C²

Question 12

Two small charged objects repel 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

Question 13

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

Question 14

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

Question 15

The diagram shows a pair of highly charged plastic cubes that attract each other. Cube 3 is a conductor and is uncharged. Which of the following illustrates the forces between cubes1 and 3 and between cubes 2 and 3?

A) I
B) II
C) III
D) IV
E) V

Question 16

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

Question 17

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 ball

Question 18

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

Question 19

Consider the following procedural steps: 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

Question 20

The charge on a glass rod which 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

Question 21

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

Question 22

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:

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

Question 23

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 m
B) 0.23 m
C) 0.62 m
D) 1.6 m
E) 4.4 m

Question 24

Charge is distributed uniformly on the surface of a spherical nonconducting shell. A point particle with charge q is inside. The electrical force on the particle q is least when:

A) it is near the inside surface of the shell
B) it is at the center of the shell
C) it is halfway between the shell center and the inside surface
D) it is near, but not at, the center of the shell
E) all of the above (the force is zero everywhere inside)

Question 25

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)
D) a/2
E)

Question 26

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)

Question 27

Two identical conducting spheres A and B carry equal charge and exert electrostatic forces of magnitude F on each other. 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 becomes:

A) F/2
B) F/4
C) 3F/8
D) F/16
E) 0

Question 28

If excess charge is put on a spherical conductor,

A) it remains where it was placed
B) it spreads a little from where it was placed but not over the whole sphere
C) it spreads uniformly over the surface of the sphere if the sphere is small
D) it spreads uniformly throughout the volume of the conductor
E) it spreads uniformly over the surface of the sphere

Question 29

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 (1/4 $\pi$$\varepsilon$ ₀) 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

Question 30

To what types of electrically charged objects does Coulomb's law apply?

A) only pointlike particles
B) any symmetric objects
C) it applies to all such objects
D) only pointlike particles and objects that can be treated as particles
E) it applies to all such objects as long as they are not moving

Question 31

A 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 q can be calculated by Coulomb's law:

A) if you use R for the distance
B) if you use 2R for the distance
C) if you use 2 $\pi$ R for the distance
D) and the result of the calculation is zero
E) none of the above

Question 32

A particle with charge 2 $\mu$ C 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

Question 33

Two particles, each with charge Q, and a third particle, with a 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

Question 34

Two protons (p₁ and p₂) and an electron (e) lie on a straight line, as shown. The directions of the force of p₁ on e, the force of p₂ on e, and the total force on e, respectively, are:

A) $\rightarrow$ , $\leftarrow$ , $\rightarrow$
B) $\leftarrow$ , $\rightarrow$ , $\rightarrow$
C) $\rightarrow$ , $\leftarrow$ , $\leftarrow$
D) $\leftarrow$ , $\rightarrow$ , $\leftarrow$
E) $\leftarrow$ , $\leftarrow$ , $\leftarrow$

Question 35

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)

Question 36

Two electrons (e₁ and e₂) and a proton (p) lie on a straight line, as shown. The directions of the force of e₂ on e₁, the force of p on e₁, and the total force on e₁, respectively, are:

A) $\rightarrow$ , $\leftarrow$ , $\rightarrow$
B) $\leftarrow$ , $\rightarrow$ , $\rightarrow$
C) $\rightarrow$ , $\leftarrow$ , $\leftarrow$
D) $\leftarrow$ $\rightarrow$ , $\leftarrow$
E) $\leftarrow$ , $\leftarrow$ , $\leftarrow$

Question 37

A 5.0-C charge is 10 m from a -2.0-C charge. The electrostatic force is 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
E) none of these

Question 38

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

Question 39

Particle 1 with charge q₁, and particle 2, with a charge q_2, are on the x axis, with particle 1 at x = a with 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

Question 40

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 q is greatest when:

A) it is just outside the 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)

Question 41

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

Question 42

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

Question 43

The magnitude of the total negative charge on the electrons in 1 mol of helium (atomic number 2, atomic 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

Question 44

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

Question 45

Which of the following is NOT a possible value for the electric charge on an object?

A) 8 x 10^-20 C
B) 8 x 10^-19 C
C) 8 x 10^-18 C
D) 8 x 10^-17 C
E) 8 x 10^-16 C

Question 46

A kiloampere .hour is a unit of:

A) current
B) charge per time
C) power
D) charge
E) energy

Question 47

If excess charge is put on a spherical nonconductor,

A) it remains where it was placed
B) it spreads a little from where it was placed but not over the whole sphere
C) it spreads uniformly over the surface of the sphere if the sphere is small
D) it spreads uniformly throughout the volume of the conductor
E) it spreads uniformly over the surface of the sphere

Question 48

Is it ever possible for the following process to occur? γ → e⁺ + e^- + e⁺

A) Yes, it is.
B) No, this process does not conserve energy.
C) No, this process does not conserve momentum.
D) No, this process does not conserve mass.
E) No, this process does not conserve electric charge.

Question 49

One type of medical imaging process is called positron emission tomography. Radioactive material is injected into a patient; during the radioactive decay the material emits a positron, which then interacts with an atomic electron, emitting gamma rays, which are detected by the imager. This gamma ray emission process is called:

A) pair production
B) annihilation
C) absorption
D) alpha decay
E) fission

Question 50

A nucleus of carbon 14 has 6 protons and 8 neutrons. The atomic number and mass number of carbon 14 are, respectively,

A) 6 and 8
B) 6 and 14
C) 8 and 14
D) 14 and 20
E) 14 and 22

Question 51

A wire contains a steady current of 2 A. The charge that passes a cross section in 2 s is:

A) 3.2*10^-19 C
B) 6.4 *10^-19 C
C) 1 C
D) 2 C
E) 4 C

Question 52

The magnitude of the total negative charge on the electrons in 1 kg of helium (atomic number 2, atomic mass 4) is:

A) 48 C
B) 2.4 * 10⁷ C
C) 4.8 * 10⁷ C
D) 9.6 * 10⁷ C
E) 1.9 *10⁸ C