PHY132 Practice Final

An electron moving in the direction of the +x-axis enters a magnetic field. If the electron experiences a magnetic deflection in the -y direction, the direction of the magnetic field in this region points in the direction of the

- z axis

An electron moving in the direction of the +x-axis enters a magnetic field. If the electron experiences a magnetic deflection in the -y direction, the direction of the magnetic field in this region points in the direction of the

-z axis

A resistor, an inductor, and a capacitor are connected in series to an AC source. The AC source is operating at the resonance frequency. Which of the following statements are true? 1. The current is in phase with the driving voltage. 2. The peak voltage across the inductor is greater than the peak voltage across the capacitor. 3. The total voltage across the inductor and the capacitor at any instant is equal to zero. 4. The peak voltage across the resistor is equal to the peak voltage across the capacitor. 5. The peak voltage across the resistor is equal to the peak voltage across the inductor. 6. The peak voltage across the capacitor is greater than the peak voltage across the inductor.

1 & 3

Which statements are true for an electron moving in the direction of an electric field? 1. Its kinetic energy decreases as it moves in the direction of the electric field. 2. Its kinetic energy increases as it moves in the direction of the electric field. 3. Its electric potential energy increases as it goes from high to low potential. 4. Its potential energy increases as its kinetic energy decreases. 5. Its electric potential energy decreases as it goes from high to low potential.

1 3 4 electric field directs from higher to lower potential. As the electron moves in the direction of the field it moves from higher to lower potential, and the velocity decreases as a result which causes kinetic energy to decrease. decrease in kinetic energy leads to an increase in potential energy (conservation of energy in a system)

Three particles travel through a region of space where the magnetic field is out of the page, as shown in the figure. The electric charge of each of the three particles is, respectively, (See picture)

1 is negative, 2 is neutral, 3 is positive

An inductor is connected in series to a fully charged capacitor. Which of the following statements are true?

1. As the capacitor is discharging, the current is increasing. 2. The stored electric field energy can be equal to the stored magnetic field energy. 3. The stored electric field energy can be greater than the stored magnetic field energy. 4. The stored electric field energy can be less than the stored magnetic field energy.

Which of the following statements are true about electric fields?

1. In a uniform electric field, the field lines are straight, parallel, and uniformly spaced 2. Electric field lines near a positive point charge radiate outward 3. the electric force acting on a point charge is proportional to the magnitude of the point charge

Consider a magnetic force acting on an electric charge in a uniform magnetic field. Which of the following statements are true?

1. The direction of the magnetic force acting on a moving charge in a magnetic field is perpendicular to the direction of the field. 2. also perpendicular to the direction of motion 3. A magnetic force is exerted on a electric charge moving through a uniform magnetic field. 4. an electric charge moving perpendicular to a magnetic field experiences a magnetic force

Which of the following statements about Gauss's law are correct? (There may be more than one correct choice.) 1. If there is no charge inside of a Gaussian surface, the electric field must be zero at points of that surface. 2. If a Gaussian surface is completely inside an electrostatic conductor, the electric field must always be zero at all points on that surface. 3. Only charge enclosed within a Gaussian surface can produce an electric field at points on that surface. 4. Gauss's law is valid only for symmetric charge distributions, such as spheres and cylinders. 5. The electric flux passing through a Gaussian surface depends only on the amount of charge inside that surface, not on its size or shape.

2 & 5

Which of the following statements are true? 1. Two positive charges attract each other. 2. Electric charge is conserved. 3. Two negative charges repel each other. 4. A neutral object contains no charge carriers. 5. Electric charge is quantized. 6. A positive charge and a negative charge attract each other.

2 3 5 6 quantized means that when something has a charge we can say that it is how many times the charge of a single electron

Five point charges q and four Gaussian surfaces S are shown. What is the total electric flux through surface S4?

2q/e0

A capacitor is charging in a simple RC circuit with a dc battery. Which one of the following statements about this capacitor is accurate? 1. There is a magnetic field between the capacitor plates because charge travels between the plates by jumping from one plate to the other. 2. There is no magnetic field between the capacitor plates because no charge travels between the plates. 3. There is a magnetic field between the capacitor plates, even though no charge travels between them, because the electric flux between the plates is changing. 4. There is a magnetic field between the capacitor plates, even though no charge travels between them, because the magnetic flux between the plates is changing. 5. The magnetic field between the capacitor plates is increasing with time because the charge on the plates is increasing.

3

Which one of the phasor diagrams shown below best represents a series LRC circuit driven at resonance?

3 at resonance, VL=VC & VC leads resistor VL lags resistor

Which of the following statements are true? 1. Kirchhoff's junction rule is based on the conservation of energy. 2. Kirchhoff's loop rule is based on the conservation of charge. 3. At any junction point in a circuit, the sum of all the currents entering the junction must equal the sum of all the currents leaving the junction. 4. The sum of the changes in potential around any closed loop of a circuit must equal zero.

3 & 4 junction rule based on conservation of charge and loop rule based on conservation of energy

Two point charges Q 1 and Q 2 of equal magnitudes and opposite signs are positioned as shown in the figure. Which of the arrows best represents the net electric field at point P due to these two charges? (see picture)

A (negative charge attracts more than positive charge repels because of the distance)

In the circuit shown in the figure, all the lightbulbs are identical. Which of the following is the correct ranking of the brightness of the bulbs?

A is the brightest, and B and C have equal brightness but less than A.

Which of the following statements about inductors are correct?

An inductor always resits any change in the current flowing through it

The figure shows three metal coils labeled A, B, and C heading towards a region where a uniform static magnetic field exists. The coils move with the same constant velocity and all have the same resistance. Their relative sizes are indicated by the background grid. As they enter the magnetic field the coils will have an induced electric current in them. For which coil will the current be the greatest?

C

Three equal negative point charges are placed at three of the corners of a square of side d as shown in the figure. Which of the arrows represents the direction of the net electric field at the center of the square?

C, charges at opposite corners cancel

A disk with a radius of R is oriented with its normal unit vector at an angle Θ with respect to a uniform electric field. Which of the following represent the electric flux through the disk?

Electric flux thru disk = E*(piR^2)cos(theta) E*(piR^2)sin(phi) sin of angle between normal and orientation cos of angle between E and orientation

A point charge Q is located a short distance from a point charge 3Q, and no other charges are present. If the electrical force on Q is F, what is the electrical force on 3Q?

F F = kQ1Q2/d^2, force depends on the magnitude of both charges already so will be the same on both

If the electric flux through a closed surface is zero, the electric field at points on that surface must be zero. (T/F)

False

A positive charge is moved from point A to point B along an equipotential surface. How much work is performed or required in moving the charge?

No work is performed or required in moving the positive charge from point A to point B

Ions having equal charges but masses of M and 2M are accelerated through the same potential difference and then enter a uniform magnetic field perpendicular to their path. If the heavier ions follow a circular arc of radius R, what is the radius of the arc followed by the lighter?

R/sqrt(2) R is inversely proportional to sqrt(mass)

Two charged objects are separated by some distance. The charge on the first object is greater than the charge on the second object. How does the force between the two objects compare?

The charged objects exert electrostatic forces on each other that are equal in magnitude and opposite in direction.

A charged particle enters into a uniform magnetic field such that its velocity vector is perpendicular to the magnetic field vector. Ignoring the particle's weight, what type of path will the particle follow?

The charged particle will follow a circular path

A long straight conductor has a constant current flowing to the right. A wire rectangle is situated above the wire, and also has a constant current flowing through it (as shown in the figure). What is true about the net force and torque on the wire?

The net magnetic force on the wire rectangle is downward, and the net torque on it is zero.

An uncharged conductor has a hollow cavity inside of it. Within this cavity there is a charge of +10µC that does not touch the conductor. There are no other charges in the vicinity. Which statement about this conductor is true? (There may be more than one correct choice.)

The outer surface of the conductor contains +10µC of charge and the inner surface contains -10µC

Suppose a region of space has a uniform electric field, directed towards the right, as shown in the figure. Which statement about the electric potential is true?

The potential at points A and B are equal, and the potential at point C is lower than the potential at point A. field lines point in the direction of lower voltages, positive charges will move toward this lower voltage and therefore have lower potential

A conducting sphere contains positive charge distributed uniformly over its surface. Which statements about the potential due to this sphere are true? All potentials are measured relative to infinity. 1. The potential at the center of the sphere is zero. 2. The potential at the surface is higher than the potential at the center. 3. The potential is lowest, but not zero, at the center of the sphere. 4. The potential at the center of the sphere is the same as the potential at the surface. 5. The potential at the center is the same as the potential at infinity.

The potential at the center of the sphere is the same as the potential on the surface of the sphere

A solid conducting sphere is placed in an external uniform electric field. With regard to the electric field on the sphere's interior, which statement is correct?

There is no electric field on the interior of the conducting sphere

An ac source of period T and voltage amplitude Vmax is connected to a single unknown ideal element that is either a resistor, an inductor, or a capacitor. At time t = 0 the voltage is zero. At time t = T/4 the current in the unknown element is equal to zero and the voltage is V = + Vmax. At time t = T/2 the current is I = −Imax , where Imax is the current amplitude. What is the unknown element?

a capacitor

A resistor and a capacitor are connected in series across an ideal battery having a constant voltage across its terminals (a)At the moment contact is made with the battery the voltage across the capacitor is (b) At the moment contact is made with the battery the voltage across the resistor is A resistor and an ideal inductor are connected in series to an ideal battery having a constant terminal voltage V0. (c) At the moment contact is made with the battery, the voltage across the resistor is (d) At the moment contact is made with the battery, the voltage across the inductor is

a) zero b) equal to the battery's terminal voltage, V0 c) equal to the battery's terminal voltage, V0 d) zero, inductor behaves as an open circuit

A circular loop of wire lies flat on a level table top in a region where the magnetic field vector points straight upward. The magnetic field suddenly vanishes. As viewed from above, in what direction does the induced current flow in the loop of wire?

an induced current flows counterclockwise in the loop

A positive point charge Q is fixed on a very large horizontal frictionless tabletop. A second positive point charge q is released from rest near the stationary charge and is free to move. Which statement best describes the motion of q after it is released?

as it moves farther and farther from Q, its speed will keep increasing initial repulsion causes an acceleration which, though decreasing, causes an always increasing velocity on a friction less surface

A resistor is connected across an AC source. Which of the following graphs shows the instantaneous current through the resistor and the instantaneous voltage across the resistor?

both i and v are cosine waves but i has a larger amplitude i and v across the resistor should be in phase

Under electrostatic conditions, the electric field just outside the surface of any charged conductor

is always perpendicular to the surface of the conductor

A circular loop of wire lies in the plane of the paper. An increasing magnetic field points out of the paper. What is the direction of the induced current in the loop?

clockwise

An electron is traveling horizontally toward the north in a uniform magnetic field that is directed vertically downward. In what direction does the magnetic force act on the electron?

east (consider downward to mean -k and north to mean +j directions)

In the figure, two parallel wires carry currents of magnitude I in opposite directions. A rectangular loop is midway between the wires. The current I is decreasing with time. The induced current through the resistor R is

from b to a (current is decreasing! current will oppose change)

In the figure, two solenoids are side by side. The switch S, initially open, is closed. The induced current through the resistor R is

from b to a current in the first flows from a to b, current in the second will oppose and flow from b to a

in the figure, a conducting rod is shown moving to the right along U-shaped conducting rails. The apparatus is in a uniform magnetic field perpendicular to the plane of the figure. As viewed from above, in what direction does the induced current flow in the U-shaped apparatus?

induced current will flow counterclockwise

Which of the following statements are true concerning electromagnetic induction? it is possible to induce a current in a closed loop of wire...

it is possible to induce a current in a closed loop of wire... 1. located in a uniform magnetic field by either increasing or decreasing area 2. by changing the strength of a magnetic field enclosed by the wire 3. without the use of a power supply or battery 4. by changing the orientation of the field enclosed by the wire

The long straight wire in the figure carries a current I that is decreasing with time at a constant rate. The circular loops A, B, and C all lie in a plane containing the wire. The induced emf in each of the loops A, B, and C is such that

loop A has a counter-clockwise emf, loop B has no induced emf, and loop C has a clockwise emf

A circular loop of wire lies flat on a level table top. A bar magnet is held stationary above the circular loop with its north pole point downward. As viewed from above, in what direction does the induced current flow in the loop of wire?

no current is induced in the wire magnet is stationary so there is no change in flux

When electric current is flowing in a metal, the electrons are moving

none of the above..... does not move @ speed of sound in air speed of light nearly speed of light speed of sound in metal

The figure shows two unequal point charges, q and Q, of opposite sign. Charge Q has greater magnitude than charge q. In which of the regions X, Y, Z will there be a point at which the net electric field due to these two charges is zero?

only field X

Five point charges q and four Gaussian surfaces S are represented in the figure shown. Through which of the Gaussian surfaces are the total electric flux zero? (see picture)

s1 and s3

A light bulb is connected in the circuit shown in the figure with the switch S open. All the connecting leads have no appreciable resistance and the battery has no internal resistance. When we close the switch, what is true about the brightness of the bulb and potential drop over R1 & R2?

the brightness of the bulb will increase and the potential drop across R2 will decrease (switch connects resistors in parallel which will decrease total resistance)

The figure shows three identical lightbulbs connected to a battery having a constant voltage across its terminals. What happens to the brightness of lightbulb 1 when the switch S is closed?

the brightness will increase permanently

When an LRC series circuit is at resonance, which one of the following statements about that circuit is accurate?

the current amplitude is a maximum

If the resistance in a circuit connected to a constant current is halved, how is the voltage in the circuit affected?

the voltage is reduced by a factor of 2 V= IR

A bar magnet is held vertically with its upper end a little bit below the center of a horizontal metal ring. The upper end of the magnet is its north pole, as shown in the figure. The bar magnet is now dropped. An observer views the ring from above its center. To this observer, how will the induced current in the ring behave as the magnet falls?

the current will flow counter clock-wise and be decreasing

Two long parallel wires are placed side by side on a horizontal table. The wires carry equal currents in the same direction. Which of the following statements are true?

the magnetic force between the two wires is attractive and the field midway between the wires is 0

When a point charge of +q is placed on one corner of a square, an electric field strength of 2 N/C is observed at the center of the square. Suppose three identical charges of +q are placed on the remaining three corners of the square. What is the magnitude of the net electric field at the center of the square?

the magnitude of the net electric field at the center of the square is 0 N/C

Two very long parallel wires are a distance d apart and carry equal currents in opposite directions. The locations where the net magnetic field due to these currents is equal to zero are

the net magnetic field is not zero anywhere

A vertical wire carries a current straight down. To the east of this wire, the magnetic field points

towards the south

An electron is initially moving to the right when it enters a uniform electric field directed upwards. Which trajectory shown below will the electron follow?

trajectory Z (electron is negative so it experiences a force which is opposite the direction of the electric field)

A negatively charged particle is moving to the right, directly above a wire having a current flowing to the right, as shown in the figure. In which direction is the magnetic force exerted on the particle?

upward

Is it possible for the electric field between two positive charges to equal zero along the line joining the two charges?

yes, regardless of the magnitude of the charges