Deck 21: Electric Charge

Question 1

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

Answer 1

electroscope leaves will tend to collapse

Question 2

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

Answer 2

contains ions

Question 3

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

Answer 3

none of the above

Question 4

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 5

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 6

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 7

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 8

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 9

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 10

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 11

The diagram shows a pair of heavily 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 12

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 13

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 14

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 15

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

Question 16

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 17

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 18

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 19

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 20

Two electrons (e₁ and e₂) and an protin (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 21

A kiloampere . hour is a unit of:

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

Question 22

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 23

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 24

Particles 1, with charge q₁ and 2, with a charge q₂ 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 25

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 26

A charge Q is spread uniformly along the circumference of a circle of radius R. A point particlewith 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) just use R for the distance
B) just use 2R for the distance
C) just use 2 $\pi$ R for the distance
D) result of the calculation is zero
E) none of the above

Question 27

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

Question 28

The diagram shows two pairs of heavily 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 29

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 30

Two particles A and B have identical charge Q. For a net force of zero to be exerted on a third chargeparticle 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 31

A particle with charge 2 $\degree$ C charge 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 32

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 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) Parrallel to the left side of the triangle
B) Parrallel to the right side of the triangle
C) Parrallel 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

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 *10⁸ C
E) 1.9 *10⁸ C

Question 35

Two particles, X and Y, are 4 m apart. X has a charge of 2Q and Y has a charge of Q. The force on X to that on Y is:

A) has twice the magnitude of the force of X on Y
B) has half the magnitude of the force of Y on X
C) has four time 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

Question 36

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

Question 37

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 38

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 39

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 40

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 41

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 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)

Question 42

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 q 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)

Question 43

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 44

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 45

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 m
E) 4.4 m