PHYS 132- EXAM 1

Consider a spot that is located midway between two identical point charges. Which one of the following statements concerning the electric field and the electric potential at this spot is true? (a)The electric field is zero, but the electric potential is not zero. (b)The electric field is not zero, but the electric potential is zero. (c)Both the electric field and the electric potential are zero. (d)Neither the electric field nor the electric potential is zero.

(a)The electric field is zero, but the electric potential is not zero.

An ion, starting from rest, accelerates from point A to point B due to a potential difference between the two points. Does the electric potential energy of the ion at point depend on (a) the magnitude of its charge and (b) its mass? Does the speed of the ion at depend on (c) the magnitude of its charge and (d) its mass?

(a)Yes. (b)No. (c)Yes. (d)Yes.

Imagine that you are moving a positive test charge along the line between two identical point charges. With regard to the electric potential, is the midpoint on the line analogous to the top of a mountain or the bottom of a valley when the two point charges are (a) positive and (b) negative?

(a)bottom of a valley (b)top of a mountain

A positive test charge is placed in an electric field. In what direction should the charge be moved relative to the field, so that the charge experiences a constant electric potential? The charge should be moved (a)perpendicular to the electric field, (b)in the same direction as the electric field, (c)opposite to the direction of the electric field.

(a)perpendicular to the electric field,

An electric potential energy exists when two protons are separated by a certain distance. Does the electric potential energy increase, decrease, or remain the same (a) when both protons are replaced by electrons, and (b) when only one of the protons is replaced by an electron?

(a)remains the same (b)decreases

Identical point charges are fixed to diagonally opposite corners of a square. Where does a third point charge experience the greater force? (a)At the center of the square (b)At one of the empty corners (c)The question is unanswerable because the polarities of the charges are not given.

(b)At one of the empty corners

Object A and object B are each electrically neutral. Two million electrons are removed from object A and placed on object B. Expressed in coulombs, what is the resulting charge (algebraic sign and magnitude) on object A and on object B?

+3.2 x 10^13 and -3.2 x 10^13

The drawing shows a cross-sectional view of two spherical equipotential surfaces and two electric field lines that are perpendicular to these surfaces. When an electron moves from point A to point B (against the electric field), the electric force does 3.2 x 10^-19 of work. What are the electric potential differences (a) vb - va b) Vc- Vb C) Vc- Va

2.0 0 2.0

A rod made from insulating material carries a net charge (which may be positive or negative), whereas a copper sphere is electrically neutral. The rod is held close to the sphere but does not touch it. Which one of the following statements concerning the forces that the rod and sphere exert on each other is true? (a)The forces are always attractive. (b)The forces are always repulsive. (c)The forces are attractive when the rod is negative and repulsive when it is positive. (d)The forces are repulsive when the rod is negative and attractive when it is positive. (e)There are no forces.

A) the forces are always attractive

How is the electric potential related to work?

An electric potential is the amount of work needed to move a unit of positive charge from a reference point to a specific point inside the field without producing an acceleration Directly proportional

What are equipotential surfaces?

Any surface over which the potential is constant is called an equipotential surface. The electric force neither helps nor hinders motion of an electric charge along an equipotential surface.

what is an electric field

Area around electric charge exerts force on other charges in the field, attracting or repelling them.

What is the capacitor equation?

C=Q/V

What is the equation for the capacitance of a parallel plate capacitor?

C=ε0A/d

What is capacitance?

Capacitance is the ratio of the change in an electric charge in a system to the corresponding change in its electric potential

what are conductors and insulators

Conductors let electricity pass through while insulators keep electricity from moving.

What is the equation for the electric field in a parallel plate capacitor?

E = σ/ε

what is the equation for the electric field related to the electrostatic force

E=F/q

what is the equation for the electric field due to a point charge?

E=kq/r^2

What are the equations for the energy stored in the capacitor?

EPE= ½CV^2

how is the electric field related to the electrostatic force?

Electric field is defined as the electric force per unit charge. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge.

How are equipotential surfaces and electric field lines related?

Electric field lines are always perpendicular to an equipotential surface

How is the electric field related to the electric field line?

Electric field lines provide a means to visualize the electric field. Electric field lines have arrows showing the direction of the electric field

What are electric field lines and what do they represent?

Electric field lines provide a means to visualize the electric field. Since the electric field is a vector, electric field lines have arrows showing the direction of the electric field. The lines are directed away from positively charged source charges and toward negatively charged source charges.

What is the electric flux and how is it related to Gauss' Law?

Electric flux is the measure of the electric field through a given surface, although an electric field in itself cannot flow. The total of the electric flux out of a closed surface is equal to the charge enclosed divided by the permittivity.

How is the electric potential related to the electric potential energy?

Electric potential is the amount of potential energy per unit of charge. ... When work is done on a positive test charge to move it from one location to another, potential energy increases and electric potential increases

Why is the surface of a conductor an equipotential surface?

Equipotential lines are perpendicular to electric field lines in every case. ... This implies that a conductor is an equipotential surface in static situations. There can be no voltage difference across the surface of a conductor, or charges will flow

What is Coulombs law

F=kq1q2/r^2

Consider two identical, thin, and nonconducting rods, A and B. On rod A, positive charge is spread evenly, so that there is the same amount of charge per unit length at every point. On rod B, positive charge is spread evenly over only the left half, and the same amount of negative charge is spread evenly over the right half. For each rod deduce the direction of the electric field at a point that is located directly above the midpoint of the rod.

For rod A, the field points perpendicularly away from the rod. For rod B, it points parallel to the rod and is directed from the positive toward the negative half.

How can Gauss' Law be used to determine the electric flux?

Gauss' law states that the electric flux through any closed surface is equal to the total charge inside divided by ε0. If a charge distribution has a high degree of symmetry, then Gauss' law alone can be used to determine the magnitude of the electric field

Which one of the following statements is true concerning the magnitude of the electric field at a point in space? It is a measure of the total charge on the object. It is a measure of the electric force per unit charge on a test charge. It is a measure of the electric force per unit mass on a test charge. It is a measure of the electric force on any charged object. It is a measure of the ratio of the charge on an object to its mass.

It is a measure of the electric force per unit charge on a test charge.

Which one of the following statements is true concerning the strength of the electric field between two oppositely charged parallel plates? It is constant between the plates except near the edges. It is zero midway between the plates. It is a maximum midway between the plates. It is a maximum near the positively charged plate. It is a maximum near the negatively charged plate.

It is constant between the plates except near the edges.

what is the difference between the electrostatic force between like charges and opposite charges

Like charges repel each other; unlike charges attract. Thus, two negative charges repel one another, while a positive charge attracts a negative charge. The attraction or repulsion acts along the line between the two charges

A particle is attached to one end of a horizontal spring, and the other end of the spring is attached to a wall. When the particle is pushed so that the spring is compressed more and more, the particle experiences a greater and greater force from the spring. Similarly, a charged particle experiences a greater and greater force when pushed closer and closer to another particle that is fixed in position and has a charge of the same polarity. Considering this similarity, will the charged particle exhibit simple harmonic motion on being released, as will the particle on the spring?

No, because the force of the spring changes direction when the spring is stretched compared to when it is compressed, while the electrostatic force does not have this characteristic.

what ways can a neutral object become charges? How does the sign of the charge on the object relate to the charging process?

Polarization is the movement of electrons within a neutral object due to the electric field of a nearby charged object. It occurs without direct contact between the two objects. Electrons are transferred whenever there is friction between materials that differ in their ability to give up or accept electrons

How does a dielectric increase capacitance?

The capacitance of a set of charged parallel plates is increased by the insertion of a dielectric material. The capacitance is inversely proportional to the electric field between the plates, and the presence of the dielectric reduces the effective electric field.

Which one of the following statements is true concerning the electrostatic charge on a conductor? The charge is uniformly distributed throughout the volume. The charge is dispersed throughout the volume of the object and distributed according to the object's shape. The charge is confined to the surface and is uniformly distributed. Most of the charge is on the outer surface, but it is not uniformly distributed. The charge is entirely on the surface and it is distributed according to the shape of the object.

The charge is entirely on the surface and it is distributed according to the shape of the object.

what does it mean the electric charge is quantized

The charge on any object, positive or negative, is quantized, in the sense that the charge consists of an integer number of protons and electrons.

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

The electric field is zero.

How is the potential found for a collection of point charges?

The electric potential (voltage) at any point in space produced by any number of point charges can be calculated from the point charge expression by simple addition since voltage is a scalar quantity. The potential from a continuous charge distribution can be obtained by summing the contributions from each point in the source charge.

A proton and an electron are released from rest at the midpoint between the plates of a charged parallel plate capacitor (see Section 18.6). Except for these particles, nothing else is between the plates. Ignore the attraction between the proton and the electron, and decide which particle strikes a capacitor plate first.

The electron arrives at a plate first.

Which one of the following statements best describes the equipotential surfaces surrounding a point charge? The equipotential surfaces are curved planes surrounding the charge, but only one passes through the charge. The equipotential surfaces are concentric cylinders with the charge on the axis at the center. The equipotential surfaces are planes extending radially outward from the charge. The equipotential surfaces are concentric cubes with the charge at the center. The equipotential surfaces are concentric spheres with the charge at the center.

The equipotential surfaces are concentric spheres with the charge at the center.

A Gaussian surface contains a single charge within it, and as a result an electric flux passes through the surface. Suppose that the charge is then moved to another spot within the Gaussian surface. Does the flux through the surface change?

The flux does not change, as long as the charge remains within the Gaussian surface.

Which one of the following statements best explains why tiny bits of paper are attracted to a charged rubber rod? Paper is naturally a positive material. Paper is naturally a negative material. The paper becomes electrically polarized by induction. The paper acquires a net positive charge by induction. Rubber and paper always attract each other.

The paper becomes electrically polarized by induction

Which one of the following statements is true concerning the spacing of the electric field lines in the vicinity of two point charges of equal magnitude and opposite sign? The spacing is small when the magnitude of the charges is small. The spacing does not depend on the magnitude of the charges. The spacing indicates the direction of the electric field. The spacing is large when the magnitude of the charges is large. The spacing indicates the relative magnitude of the electric field.

The spacing indicates the relative magnitude of the electric field.

Which one of the following statements is true concerning the work done by an external force in moving an electron at constant speed between two points in an electrostatic field? The work done only depends on the speed of the electron. The work done depends on the total distance covered. The work done is always zero joules. The work done depends only on the displacement of the electron. The work done is always positive.

The work done depends only on the displacement of the electron.

What is the work done by the electric field when moving between two points?

The work done in taking a charge between two points in an electric field generated by fixed charges is independent of the path taken between the points. This is a conservative force

What is the equation for the potential for a point charge?

V=kq/r

How is the work done as a charge moves in an electric related to the electric potential energy?

Wab=q(Va-Vb) If q is a positive charge, then work done is positive if the charge is moved in the direction of the field.

Blow up a balloon, tie it shut, and rub it against your shirt a number of times, so that the balloon acquires a net electric charge. Now touch the balloon to the ceiling. When released, will the balloon remain stuck to the ceiling?

Yes, because the charge on the balloon will induce a slight charge of opposite polarity in the surface of the ceiling, analogous to that in Figure 18.8.

What is a capacitor?

a device used to store an electric charge, consisting of one or more pairs of conductors separated by an insulator.

What is Gauss' Law?

a law relating the distribution of electric charge to the resulting electric field. The net outward normal electric flux through any closed surface is proportional to the total electric charge enclosed within that closed surface. ϕ = Q/ϵ0

What is a dielectric?

a medium or substance that transmits electric force without conduction; an insulator. Such as rubber, plastic or waxed paper.

A positive point charge is located to the left of a negative point charge. When both charges have the same magnitude, there is no place on the line passing through both charges where the net electric field due to the two charges is zero. Suppose, however, that the negative charge has a greater magnitude than the positive charge. On which part of the line, if any, is a place of zero net electric field now located? (a)To the left of the positive charge (b)Between the two charges (c)To the right of the negative charge (d)There is no zero place.

a) to the left of the positive charge

In a region of space where the electric field is constant everywhere, as it is inside a parallel plate capacitor, is the potential constant everywhere? (a)Yes. (b)No, the potential is greatest at the positive plate. (c)No, the potential is greatest at the negative plate.

b) no, the potential is greatest at the positive plate

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)adjacent corners, (b)diagonally opposite corners.

b)diagonally opposite corners.

A charged conductor is brought near an uncharged insulator. Which one of the following statements is true? Both objects will repel each other. Neither object exerts an electrical force on the other. The objects will repel each other only if the conductor has a negative charge. Both objects will attract each other. The objects will attract each other only if the conductor has a positive charge

both objects will attract each other

An electrically neutral object acquires a net electric charge. Which one of the following statements concerning the mass of the object is true? (a)The mass does not change. (b)The mass increases if the charge is positive and decreases if it is negative. (c)The mass increases if the charge is negative and decreases if it is positive.

c

There is an electric field at point P . A very small positive charge is placed at this point and experiences a force. Then the positive charge is replaced by a very small negative charge that has a magnitude different from that of the positive charge. Which one of the following statements is true concerning the forces that these charges experience at ? (a)They are identical. (b)They have the same magnitude but different directions. (c)They have different magnitudes but the same direction. (d)They have different magnitudes and different directions.

d) they have different magnitudes and different directions

An empty parallel plate capacitor is connected to a battery that maintains a constant potential difference between the plates. With the battery connected, a dielectric is then inserted between the plates. Do the following quantities decrease, remain the same, or increase when the dielectric is inserted? (a) The electric field between the plates (b) The capacitance (c) The charge on the plates (d) The energy stored by the capacitor

decreases increases increases increases

A parallel plate capacitor is charged up by a battery. The battery is then disconnected, but the charge remains on the plates. The plates are then pulled apart. Do the following quantities decrease, remain the same, or increase as the distance between the plates increases? (a) The capacitance of the capacitor (b) The potential difference between the plates (c) The electric field between the plates (d) The electric potential energy stored by the capacitor

decreases increases remains the same increases

An electron traveling horizontally enters a region where a uniform electric field is directed upward. What is the direction of the force exerted on the electron once it has entered the field?

downward

What is the electric potential?

electric potential energy per unit charge... the amount of work needed to move a unit of positive charge from a reference point to a specific point inside the field without producing an acceleration

What is the name of unit of energy that is the amount by which the electric potential energy of an electron changes when it moves through a potential difference of one volt?

electric volt

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

energy

What is the energy density for a capacitor?

energy density= ½kε0E^2

The sketch below shows cross sections of equipotential surfaces between two charged conductors that are shown in solid grey. Various points on the equipotential surfaces near the conductors are labeled A, B, C, ..., I.

h

How does the electric field and voltage of a capacitor change with a dielectric if the charge of the capacitor is kept constant? If the voltage of the capacitor is kept constant?

if the charge of the capacitor is kept constant then the voltage reduces by a factor of k. The electric field decreases as well. If the voltage is constant then the electric field will not change and the charge increases

Complete the following statement: When an ebonite rod is rubbed with animal fur, the rod becomes negatively charged as Entry field with incorrect answer negative charges are transferred from the fur to the rod. positive charges are transferred from the rod to the fur. positive charges are transferred from the fur to the rod. negative charges are transferred from the rod to the fur. negative charges are created on the surface of the rod.

negative charges are transferred from the fur to the rod

Three point charges are fixed to the corners of a square, one to a corner, in such a way that the net electric field at the empty corner is zero. Do these charges all have (a) the same sign and (b) the same magnitude (but, possibly, different signs)?

no no

Which one of the following changes will necessarily increase the capacitance of a capacitor? Entry field with correct answer increasing the charge on the plates increasing the potential difference between the plates decreasing the charge on the plates placing a dielectric between the plates decreasing the potential difference between the plates

placing a dielectric between the plates

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)zero, (b)negative, (c)positive.

positive

The magnitude of the charge on the plates of an isolated parallel plate capacitor is doubled. Which one of the following statements is true concerning the capacitance of this parallel-plate system? The capacitance depends on the potential difference across the plates. The capacitance is decreased to one half of its original value. The capacitance is increased to twice its original value. The capacitance remains unchanged. The capacitance depends on the electric field between the plates.

the capacitance remains uncharged

What is the shielding effect of a conductor?

the conductor shields any charge within it from electric fields created outside the conductor. The shielding results from the induced charges on the conductor surface.

A proton is fixed in place. An electron is released from rest and allowed to collide with the proton. Then the roles of the proton and electron are reversed, and the same experiment is repeated. Which, if either, is traveling faster when the collision occurs, the proton or the electron?

the electron

A proton and an electron are held in place on the x axis. The proton is at x= -d , while the electron is at x= d. They are released simultaneously, and the only force that affects their motions significantly is the electrostatic force of attraction that each applies to the other. Which particle reaches the origin first?

the electron, because, being less massive, it has the greater acceleration

A parallel plate capacitor with plates of area A and plate separation d is charged so that the potential difference between its plates is V. If the capacitor is then isolated and its plate separation is decreased to d/2, what happens to the potential difference between the plates? Entry field with correct answer The final potential difference is 4V. The final potential difference is 0.25V. The final potential difference is V. The final potential difference is 0.5V. The final potential difference is 2V.

the final potential difference is 0.5 V

what is charge

the property of matter associated with electromagnetic forces. Measured in coulombs, value for electricity flowing in a circuit

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? The total electric potential energy is doubled. The total electric potential energy remains the same. The total electric potential energy increases by a factor of 4. The total electric potential energy is reduced to one-half of its original value. The total electric potential energy is reduced to one-fourth of its original value.

the total electric potential energy is doubled

The drawing shows three possibilities for the potentials at two points, A and B. In each case, the same positive charge is moved from A to B. In which case, if any, is the most work done on the positive charge by the electric force?

the work is the same in all three cases

how many types of charges are there

two, positive and negative

What is the electric field inside a conductor?

zero In electrostatics free charges in a good conductor reside only on the surface. So the free charge inside the conductor is zero