PHY 2 EX 1

Which of the following would increase the capacitance of a parallel-plate capacitor? I. Insert a dielectric between the plates. II. Increase the surface area of each plate. III. Increase the separation distance between the plates.

I and II

Consider the following four possibilities for two point charges and choose the one(s) that do not change the magnitude of the electrostatic force that each charge exerts on the other: A. Double the magnitude of each charge and double the separation between them. B. Double the magnitude of each charge and reduce the separation between them to half of its initial value. C. Double the magnitude of only one charge and double the separation between the charges. D. Double the magnitude of only one charge and increase the separation between the charges by a factor of square root of 2.

a and d Doubling the magnitude of each charge as in A would increase the numerator by a factor of four, but this is offset by the change in separation, which increases the denominator by a factor of 22 = 4. Doubling the magnitude of only one charge as in D would increase the numerator by a factor of two, but this is offset by the change in separation, which increases the denominator by a factor of (sqrt(2))^2 =2

A positive point charge and a negative point charge have equal magnitudes. One charge is fixed to one corner of a square, and the other is fixed to another corner. On which corners should the charges be placed, so that the same potential exists at the empty corners? The charges should be placed at a. diagonally b. adjacent corners

a.

An electrically neutral balloon is rubbed on cloth and becomes positively charged. What can be said about its mass? a. decreases b. increases c. doesnt change

a.

Electric field lines that are closer together represent : a. stronger magnitude b. weaker magnitude

a.

Suppose a negative point charge is placed at x=0 and an electron is placed at some point P on the positive x-axis. What is the direction of the electric field at point P due to the point charge, and what is the direction of the force experienced by the electron due to that field? a. E along -x; F along +x b. E along +x; F along -x c. E along -x; F along -x d. E along +x; F along +x

a.

The electric potential is constant throughout a certain region of space. What can you say about the electric field in this region? a. The electric field is zero. b. The electric field is non-zero.

a.

The electric potential is constant throughout a given region of space. Is the electric field zero or nonzero in this region? a. zero b. nonzero

a.

The length and width of each plate of a parallel plate capacitor are doubled, and the spacing between the plates is also doubled. By what factor does the capacitance change? a. The capacitance increases by a factor of 2. b. The capacitance decreases by a factor of 4. c. The capacitance increases by a factor of 8. d. The capacitance decreases by a factor of 2. e. The capacitance increases by a factor of 4.

a.

charge q1 is placed a distance r0 from charge q2. what happens to the magnitude of the force on q1 due to q2 if the distance is reduced to r0/4? a. force increases by factor of 16 b. force increases by factor of 4 c. force increases by factor of 2 d. force increases by factor of 8

a.

Which of the following statements is/are true? I. An equipotential surface is a surface of constant potential. II. The electrostatic force does no work on a charge that moves along an equipotential surface. III. The equipotential surfaces surrounding a point charge consist of an infinite number of concentric spherical shells. IV. Electric field lines are everywhere perpendicular to equipotential surfaces. I only I and II only III and IV only All of the above.

all the above

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 net charges on these three objects? in a, b, c order a. + + - b. - + - c. - + + d. + - - e. - - +

b.

Suppose a small, positively charged particle moves past a positively charged sphere with speed . Which one of the following vectors is parallel to the electric field lines of the sphere (at the location of the particle) the instant the particle passes the sphere? a. The displacement of the particle. b. The acceleration of the particle. c. The velocity of the particle. d. None of these.

b.

Suppose an electron is moving with a constant velocity until it encounters a positively charged sphere on its right. How does the sphere alter the trajectory of the electron? a. no effect b. deflects to the right c. deflects to the left

b.

The electric potential V is constant everywhere within a certain region of space. Which statement below is true? a. The electric field varies from place to place within the region. b. The electric field is zero everywhere within the region. c. A charged particle placed within the region will experience an electric force. d. The electric field is also constant (but not zero) within the region.

b.

Three point charges have identical magnitudes, but two of the charges are positive and one is negative. These charges are fixed to the corners of a square, one to a corner. No matter how the charges are arranged, the potential at the empty corner is always a. negative b. positive c. zero

b.

A charge of +2Q and -2Q are located at two of the vertices of an equilateral triangle. Which of the following is true? a.The potential at the triangle's empty vertex is positive. b. The potential at the triangle's empty vertex is negative. c. The potential at the triangle's empty vertex is zero.

c.

Complete the following statement: The electron volt is a unit of a.electric field strength. b.electric force. c.energy. d.electric power. e.electric potential difference.

c.

Suppose the electric field of a point charge of +5q is represented by 20 field lines directed radially outward from the charge. How should the electric field of a point charge of -10q be represented? a. 40 field lines directed radially outward b. 10 field lines directed radially outward c. 40 field lines directed radially inward d. 10 field lines directed radially inward

c.

The potential at a distance r from a positive point charge is +V. What is the potential at a distance of r/3? a. +(1/3)V b. +V c. +3V d. +9V

c.

Two different charges, q1 and q2, are placed at two different locations, one charge at each location. The locations have the same electric potential V. Do the charges have the same electric potential energy? a. No, because the electric potential V at a given location depends on the charge placed at that location, whereas the electric potential energy EPE does not. b. Yes. If the electric potentials at the two locations are the same, the electric potential energies are also the same, regardless of the type (+ or -) and magnitude of the charges placed at these locations. c. No, because the electric potential energy EPE at a given location depends on the charge placed at that location as well as the electric potential V. d. Yes, because electric potential and electric potential energy are just different names for the same concept.

c.

Two positive point charges are separated by a distance R. If the distance between the charges is reduced to R/2, what happens to the total electric potential energy of the system? a. The total electric potential energy remains the same. b. The total electric potential energy increases by a factor of 4. c. The total electric potential energy is doubled. d. The total electric potential energy is reduced to one-half of its original value. e. The total electric potential energy is reduced to one-fourth of its original value.

c.

A parallel plate capacitor is connected to a battery that maintains a constant potential difference between the plates. If the plates are pulled away from each other, increasing their separation, what happens to the amount of charge on the plates? a. Nothing happens; the amount of charge stays the same. b. The amount of the charge increases, because the capacitance decreases. c. The amount of the charge increases, because the capacitance increases. d. The amount of the charge decreases, because the capacitance decreases. e. The amount of the charge decreases, because the capacitance increases.

d.

A capacitor is charged with a battery to a voltage V and then disconnected from the battery. A dielectric is inserted between the plates. When the dielectric is inserted, what happens to the electrostatic potential energy stored in the capacitor? The stored energy increases. The stored energy decreases. The stored energy remains constant.

decreases

A -4.0-µC charge is located 0.45 m to the left of a +6.0-µC charge. What is the magnitude and direction of the electrostatic force on the positive charge? a. 4.4 N, to the right b. 2.2 N, to the left c. 1.1 N, to the right d. 2.2 N, to the right e. 1.1 N, to the left

e. F = k(-4E-6)(6E-6)/(.45)^2 force of n attraction exist between opposite charges , so the forceexpereinced by +ve charge will be towrads -ve charge , therefore it will be directed towards left

Because of an electric field, a positive charge +q experiences a force of magnitude F that points due west. The positive charge is then replaced with a negative charge -2q. What force does the negative charge experience? a. The negative charge experiences no force, because electric fields only exert forces on positive charges. b. Force magnitude = F, force direction is due east c. Force magnitude = 2F, force direction is due west d. Force magnitude = F, force direction is due west e. Force magnitude = 2F, force direction is due east

the force exerted on a charge by an electric field is proportional to the magnitude of the charge. Since the negative charge has twice the magnitude of the positive charge, the negative charge experiences twice the force. Furthermore, the direction of the force on the positive charge is in the same direction as the field, so that we can conclude that the field points due west. The force on the negative charge points opposite to the field and, therefore, points due east. e

How would you know how to tackle this problem: What is the electrostatic force between and electron and a proton separated by 0.1 mm?

use electrostatic force formula: k(e^2)/d^2 knowing k = 8.99 E 9 electron e = 1.6 E -19

how to do this problem?? The electric potential at a certain point in space is 12 V. What is the electric potential energy of a -3.0 μC charge placed at that point?

ΔU = q ΔV = -(3.0x10-6 C) (12 V) = -36.0x10-6 J