Deck 16: Electric Force and Field

Question 1

When the distance to a polar molecule is doubled, the electric field due to the dipole decreases by what factor?

A)4
B)8
C)16
D)64

Answer 1

8

Question 2

Each of two small spheres is positively charged, the combined charge being 40.0 µC. When the two spheres are 50.0 cm apart, each sphere is repelled from the other by a force of magnitude 2.0 N. What is the magnitude of the larger of the two charges?

A)38.6 µC
B)19.3 µC
C)2.0 µC
D)1.4 µC

Answer 2

38.6 µC

Question 3

Two protons in the nucleus of a helium atom are 2 × 10^-15 m apart. What is the minimum strength of the nuclear strong force of attraction that is required to hold the nucleus together against Coulomb repulsion?

A)58 N
B)29 N
C)6 N
D)1 N

Answer 3

58 N

Question 4

Which of the following did Millikan's experiment in 1909 set out to prove?

A)that droplets of oil carry a charge
B)that the inverse square property of Coulomb's law could be verified
C)that charges are quantized
D)that the constant of proportionality in Coulomb's law could be measured

Question 5

Suppose that the Moon is held in its orbit around Earth by electrical forces rather than by gravitation. Given the gravitational constant G = 6.673 × 10^-11 N m²/kg², and that the mass of Earth is 5.98 × 10²⁴ kg, and the mass of the Moon is 7.35 × 10²² kg, what electrical charges, -Q on Earth and +Q on the Moon, are necessary to hold the Moon in a circular orbit?

A)8.38 × 10¹² C
B)5.71 × 10¹³ C
C)7.02 × 10¹³ C
D)1.19 × 10¹⁴ C

Question 6

Which of these statements accurately describes latent heat is required in order to change water from the liquid to the vapour state?

A)Water molecules form a crystal structure, and it takes energy to break up this structure.
B)Molecules in the liquid phase must reach the boiling point of water before they can escape.
C)The hydrogen bonds between different water molecules must be broken to allow evaporation.
D)The additional energy is required to raise the mean speed of molecules high enough to escape the liquid.

Question 7

Which of the statement describes a hydration shell?

A)a collection of water molecules that surround a positive ion in solution
B)a collection of water molecules that surround a negative ion in solution
C)a shell of hydrogen atoms that surrounds an ion in solution
D)a collection of water molecules that surround an ion in solution

Question 8

What is the electric force on a singly charged ion that is located 5.0 × 10^-10 m away from a water molecule, along the axis of its dipole?

A)7.1 × 10^-10 N
B)3.6 × 10^-10 N
C)4.2 × 10^-11 N
D)3.6 × 10^-11 N

Question 9

Consider two copper balls, each of one molar mass, and 10.0 m apart. Suppose 0.01% of the atoms in one ball acquire an excess positive charge of +e each, and 0.01% of the atoms in the other ball acquire an excess negative charge of -e each. What is the electric force between them?

A)0.96 N
B)8.0 × 10⁵ N
C)9.6 × 10⁸ N
D)8.3 × 10⁹ N

Question 10

What is the resultant magnitude and direction of the force on a 5 µC charge, situated on the y-axis at 4.0 cm from the point of origin, due to a pair of 3 µC charges located on the x-axis at opposite sides of the point of origin, each at a distance of 3.0 cm from the point of origin?

A)108.0 N in the +y-direction
B)108.0 N in the -y-direction
C)86.4 N in the +y-direction
D)86.4 N in the -y-direction

Question 11

If you disturb the position of a test charge from its equilibrium point, located between a pair of stationary positive charges, what motion of the test charge occurs?

A)It always returns to its equilibrium position.
B)It returns to its equilibrium position if it has negative charge.
C)It moves away from its equilibrium position if it has positive charge.
D)It never returns to its equilibrium position, and the equilibrium is unstable.

Question 12

In the classical model of the hydrogen atom, the electron orbits the nucleus (proton) at a distance of 5.5 × 10^-11 m. Given that the electron's mass, 9.1 × 10^-31 kg, is negligible relative to that of the proton, what is the linear frequency (in Hz) of the orbital revolution of the electron around the proton?

A)1.04 × 10¹⁴ Hz
B)8.9 × 10¹⁴ Hz
C)2.0 × 10¹⁵ Hz
D)3.5 × 10¹⁶ Hz

Question 13

Which of the following does NOT accurately describe the mass and electric charge properties of a particle?

A)Charge is quantized into multiples of a basic unit of charge.
B)Mass cannot be negative, whereas charges can be either positive or negative.
C)The gravitational force between charged particles is larger than the electrical force.
D)Different masses always attract each other through gravity.

Question 14

If we double the charge on two point charges, and double the distance between them, how much does the electric force between them change?

A)doubled
B)halved
C)remains the same
D)four times larger

Question 15

Two parallel plates are immersed in salt water, and a battery is connected to the plates. Which of the following happens at the surface of the positively charged plate?

A)Only Na ions migrate to the plate.
B)Both Cl and Na ions migrate to the plate, with their hydration shells removed.
C)Only Cl ions migrate to the plate.
D)The hydration shells around the Na and Cl ions shield them from the electric field, so nothing happens.

Question 16

Three point charges, two positive and one negative, each having a magnitude of 10.0 µC, are placed at the vertices of an equilateral triangle that is 50.0 cm on a side. What is the magnitude of the electrostatic force on the negative charge?

A)3.1 N
B)3.6 N
C)6.2 N
D)7.2 N

Question 17

Which of the following statements accurately describes how electric field lines may be represented graphically?

A)The direction of the field is perpendicular to the line; magnitude is shown by the local density of the lines.
B)The direction of the field is perpendicular to the line; magnitude is shown by the thickness of the lines.
C)The direction of the field is tangent to the line; magnitude is shown by the local density of the lines.
D)The direction of the field is tangent to the line; magnitude is shown by the thickness of the lines.

Question 18

The surfaces of a lipid bilayer forming the membrane around a cell with a diameter of 2 µm has a residual charge of 2 × 10^-15 C on the outside of the bilayer, and the same amount of negative charge on the inside. What is the force on a singly charged positive ion located on the outer surface of this membrane?

A)6 × 10^-11 N
B)8 × 10^-12 N
C)3 × 10^-12 N
D)9 × 10^-13 N

Question 19

Four charges of +10.0 µC are placed at the four corners of a square that is 50.0 cm on each side. What is the magnitude of the electric field at the centre of the square?

A)2.9 N/C
B)2.1 N/C
C)0.7 N/C
D)0 N/C

Question 20

A charge of +40 µC is placed on the x-axis at x = 0. A second charge of -40 µC is placed on the x-axis at x = 50 cm. What is the magnitude of the electrostatic force on a third charge of 3.0 µC placed on the x-axis at x = 25 cm?

A)0.0 N
B)23.1 N
C)34.6 N
D)51.9 N

Question 21

Describe the cell membrane modelled by electrically charged plates.

Question 22

Consider two electric dipoles in empty space. Each dipole has zero net charge. Does an electric force act between the dipoles even though their net charge is zero? Explain.

Question 23

Explain what is meant by a "neutral atom," a "positively charged ion," and a "negatively charged ion."

Question 24

Freezing occurs when hydrogen bonds between water molecules begin to form.

Question 25

Ions in a salt can be modelled with an electric dipole system.

Question 26

Cell membranes can be modelled with two charged plates separated at a distance equal to the thickness of the membrane.

Question 27

The temperature of water must be above a threshold value before any hydrogen bonds are broken.

Question 28

All atomic particles carry an electric charge, either positive or negative.

Question 29

When a third charge q₀ is inserted on the line between two charges, Q₁ and Q₂, each having the same sign, the position at which q₀ is in equilibrium between Q₁ and Q₂ does not depend on the sign or magnitude of q₀.

Question 30

The reason symmetric molecules CH₄ and SiH₄ have very low boiling temperatures is that they have no dipole moment.

Question 31

Show that a dipole placed in a uniform electric field, with its axis making an angle to the direction of the field, will experience a restoring torque tending to align the dipole with the field.

Question 32

Rubber rods charged by rubbing with cat fur repel each other. Glass rods charged by rubbing with silk repel each other. A rubber rod and a glass rod charged respectively as above attract each other. A possible explanation is that all rubber rods always have an excess of positive charge on them.

Question 33

Describe how, experimentally, you could distinguish a gravitational from an electric field.

Question 34

Discuss the similarities and differences between Newton's law of gravitation and Coulomb's law.

Question 35

Two charged particles exert an electric force on each other, according to Coulomb's law. What relationship do these forces have to each other? Discuss in terms of Newton's third law.

Question 36

Figure 16.1 Electric dipole model for the water molecule.
In the water molecule (Fig. 16.1), the electric field at the midpoint, P₂, between the hydrogen atoms is directed away from the oxygen molecule.

Question 37

If an electron beam enters a region of electric field pointing upward, the beam will be bent downward in a vertical plane.

Question 38

In an electric field, the dipole axes of polar molecules align with the field so that the positively charged end points in the direction of the field.

Question 39

The electric field in the vicinity of a collection of charges, all of the same sign, can never vanish.

Question 40

Hospital personnel must wear special conducting shoes while working around oxygen in an operating room. Why? What would otherwise happen if the shoes were rubber soled?

Question 41

Material composed of polar molecules is inserted between a pair of parallel plates on which equal and opposite charges reside. What effect does the electric field of the parallel plates have on the polar molecules? Show that this is equivalent to a layer of charge forming on the surfaces of the material, of opposite sign to the charge on the adjacent plate.

Question 42

Explain why electric field lines can never cross.

Question 43

Nerve cell membranes have electric fields associated with a charge of the opposite sign on the inside and outside surfaces of the membrane. The walls of the membrane will therefore experience attraction toward each other, resulting in a compression of the membrane. Assuming there are 2 × 10⁴ charges, each of magnitude e (= 1.6 × 10^-19 C), on the membrane, and that the cell has a diameter of d = 2 µm, estimate the force per unit area of this compression.