Physics Concept Questions Ch 18,19,20,21

(19) he 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. What is the magnitude of the electric field at point A?

100 V/m

(20) Two identical resistors are connected first in series and second in parallel. The equivalent resistances of the two types of connections are, respectively, RS and RP. What is the ratio RS/RP?

4

(19) 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. What is the potential difference between points B and E?

50V

(20) The figure shows variation of the current through the heating element with time in an iron when it is plugged into a standard 120 V, 60 Hz outlet. What is the rms value of the current in this circuit?

7.1A

(20) The drawings show a number of different possibilities for connecting an ammeter (AM) and a voltmeter (VM) to a circuit, in order to measure the current in and the voltage across the resistor labeled R2. Which one of the possibilities shows the correct connections?

A

(19) The drawing shows three arrangements of charged particles, all the same distance from the origin. Rank the arrangements, largest to smallest, according to the total electric potential V at the orig

A and C (a tie), B

(18) 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 sqrt 2.

A and D

(20) A single resistor is connected across the terminals of a battery. Which one or more of the following changes in voltage and current leaves unchanged the electric power dissipated in the resistor? (A) Doubling the voltage and reducing the current by a factor of two. (B) Doubling the voltage and increasing the resistance by a factor of four. (C) Doubling the current and reducing the resistance by a factor of four.

A, B, C

(18) Three point charges have equal magnitudes and are fixed to the corners of an equilateral triangle. Two of the charges are positive and one is negative, as the drawing shows. At which one of the corners is the net force acting on the charge directed parallel to the x axis?

B

(18) Three point charges have equal magnitudes and are located on the same line. The separation d between A and B is the same as that between B and C. One of the charges is positive and two are negative, as the drawing shows. Consider the net electrostatic force that each charge experiences due to the other two charges. Rank the net forces in descending order (greatest first) according to magnitude.

B,A,C

(18) The drawing shows some electric field lines. For the points indicated, rank the magnitudes of the electric field in descending order (largest first).

B,C,A

(20) In the following three arrangements each resistor has the same resistance R. Rank the equivalent resistances of the arrangements in descending order (largest first).

B,C,A

(20) Which one of the following graphs correctly represents Ohm's law, where V is the voltage and I is the current?

C

(19) The drawing shows edge-on views of three parallel plate capacitors with the same separation between the plates. The potential of each plate is indicated above it. Rank the capacitors as to the magnitude of the electric field inside them, largest to smallest.

C,B,A

(18) The drawings show (in cross section) two solid spheres and two spherical shells. Each object is made from copper and has a net charge, as the plus and minus signs indicate. Which drawing correctly shows where the charges reside when they are in equilibrium

D

(19) The drawing shows a plot of the electric potential V versus the displacement s. The plot consists of four segments. Rank the magnitude of the electric fields for the four segments, largest to smallest.

D, B, A and C (a tie)

(18) The drawing shows an electric field line. What are the directions of the electric fields at points A, B, and C

Due south at A, southeast at B, due east at C

(18) 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?

Force magnitude = 2F, force direction is due east

(19) 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. At which of the labeled points will an electron have the greatest potential energy?

H

(19) 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. At which of the labeled points will the electric field have the greatest magnitude?

I

(18) Each of two identical objects carries a net charge. The objects are made from conducting material. One of them is attracted to a positively charged ebonite rod, and the other is repelled by the rod. After the objects are touched together, it is found that they are each repelled by the rod. What can be concluded about the initial charges on the objects?

Initially one object is positive and one is negative, with the positive charge having a greater magnitude than the negative charge.

(18) 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.

(19) 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?

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.

(18) Only one of three balls A, B, and C carries a net charge q. The balls are made from conducting material and are identical. One of the uncharged balls can become charged by touching it to the charged ball and then separating the two. This process of touching one ball to another and then separating the two balls can be repeated over and over again, with the result that the three balls can take on a variety of charges. Which one of the following distribution of charges could not possibly be achieved in this fashion, even if the process were repeated an infinite number of times?

Qa= 1/2q, Qb=3/8q, Qc= 1/4q

(20) When applying Kirchhoff's rules, one of the essential steps is to mark each resistor with plus and minus signs to label how the potential changes from one end of the resistor to the other. The circuit in the drawing contains four resistors, each marked with the associated plus and minus signs. However, one resistor is marked incorrectly. Which one is it?

R4

(20) A battery has an emf of V and an internal resistance of r. What resistance R, when connected across the terminals of this battery, will cause the terminal voltage of the battery to be one-halfUpper V?

R=r

(19) Two positive charges are located at points A and B as shown in the figure. The distance from each charge to the point P is a = 2.0 m.

Suppose that the charges are rearranged as shown in this figure. Which one of the following statements is true for this new arrangement?

(19) 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?

The capacitance increases by a factor of 2.

(19) 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 its capacitance?

The capacitance is twice its original value.

(19) A proton is released from rest at point A in a constant electric field and accelerates to point B (see part a of the drawing). An electron is released from rest at point B and accelerates to point A (see part b of the drawing). How does the change in the proton's electric potential energy compare with the change in the electron's electric potential energy?

The change in the proton's electric potential energy is the same as the change in the electron's electric potential energy.

(19) The drawing shows two different charge configurations, but in each case a charge q is located at the origin. A charge q0 is placed a distance r from the origin (top drawing), and a charge 2q0 is placed a distance 2r from the origin (bottom drawing). All charges are positive. Which statement is true regarding the electric potential energy EPE (not the electric potential V) of the charges in the top drawing relative to those in the bottom drawing?

The charges in the top drawing have the same electric potential energy as those in the

(19) The electric potential V is constant everywhere within a certain region of space. Which statement below is true?

The electric field is zero everywhere within the region

(19) A point charge q is located at the origin. A charge q0 can be placed at a point P1, which is a distance r from the origin (top drawing). Or, a charge 2q0 can be placed at P2, which is a distance 2r from the origin (bottom drawing). All charges are positive. Which statement is true about the electric potentials due charge q at P1 and P2?

The electric potential at P1 is greater than that at P2, because r is smaller than 2r.

(19) Which one of the following statements is true after the spheres are connected by the wire

The electric potential of A equals that of B.

(19) Which one of the following statements best describes the equipotential surfaces surrounding a point charge?

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

(19) 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?

The final potential difference is 0.5V.

(18) Three point charges (some positive and some negative) are fixed to the corners of the same square in various ways, as the drawings show. Each charge, no matter what its algebraic sign, has the same magnitude. In which arrangement (if any) does the net electric field at the center of the square have the greatest magnitude?

The magnitude of the net field at the center of the square is the same in each arrangement of the ch

(18) The figure shows the electric field lines in the vicinity of two point charges. Which one of the following statements concerning this situation is true?

The magnitude of the ratio (q2/ q1) is less than one.

(20) Which one of the following statements concerning resistance is true?

The resistance of a metal wire changes with temperature.

(18) A positively charged ebonite rod is brought close to a small ball. The rod does not touch the ball, which is made from a conducting material. The ball is electrically neutral. Which one of the following statements is true?

The rod attracts the ball.

(19) 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.

(18) Each of three objects carries a charge. As the drawing shows, objects A and B attract each other, and objects C and A also attract each other. Which one of the following statements concerning objects B and C is true?

They repel each other

(18) The drawing shows a positive and a negative point charge. The negative charge has the greater magnitude. Where on the line that passes through the charges is the one spot where the total electric field is zero?

To the left of the positive charge.

(18) You have two identical metal spheres and a negatively charged ebonite rod. Without touching the rod to the spheres, which one of the following procedures can you use to give each sphere a net electrical charge of the same magnitude, one being positive and the other being negative.

Touch the two spheres together. Bring the rod near one sphere, opposite the place where the spheres are touching. Then, with the rod in place, separate the spheres.

(20) The resistance of a resistor-capacitor combination is reduced to one-third of its initial value. What must be done to the capacitance, in order that the time constant of the circuit remains unchanged?

Triple the capacitance.

(20) For the circuit shown in the drawing, what is the voltage V1 across resistance R1?

V 1 equals (R 1/ R 1 + R 2) V

(20) Which one of the following situations results in a conventional electric current that flows northward?

a beam of electrons moves southward

(19) 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. A positive point charge is placed at F. Complete the following statement: When it is released,

a force will cause it to move away from E.

(19) Complete the following statement: The electron volt is a unit of

energy

(20) Complete the following statement: The unit kilowatt · hour measures

energy

(19) A positive charge is moving from point A to point B in a uniform electric field, as shown in the drawing. The electric force does __________ work on the charge and, as a consequence, its electric potential energy __________ .

negative, increases

(18) A positive point charge q1 creates an electric field of magnitude E1 at a spot located at a distance r1 from the charge. The charge is replaced by another positive point charge q2, which creates a field of magnitude E2 = E1 at a distance of r2 = 2r1. How is q2 related to q1?

q2 = 4q1

(20) For the circuit shown in the drawing, what is the ratio of the current I1 in resistor R1 to the current I2 in resistor R2?

t1/t2= R2/R1

(19) Complete the following statement: When a dielectric with constant κ is inserted between the plates of a charged isolated capacitor

the electric field between the plates is reduced by a factor of κ.

(20) Complete the following statement: The electromotive force is

the maximum potential difference between the terminals of a battery.

(19) 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. What is the direction of the electric field at B?

toward D

(18) Five particles are shot from the left into a region that contains a uniform electric field. The numbered lines show the paths taken by the five particles. A negatively charged particle with a charge -3Q follows path 2 while it moves through this field. Do not consider any effects due to gravity.

toward the bottom of the page

(18) A cubical Gaussian surface is placed in a uniform electric field as shown in the figure. The length of each edge of the cube is 1.0 m. The uniform electric field has a magnitude of 5.0 × 108 N/C and passes through the left and right sides of the cube perpendicular to the surface. What is the total electric flux that passes through the

zero N·m2/C