Deck 20: Electric Fields and Forces

Question 1

Two electrons are passing 26.0 mm apart.What is the electric repulsive force that they exert on each other? (The value of k is 9.0 × 10⁹ N·m²/C². )

A)3.4 × 10^-25 N
B)1.3 × 10¹⁰ N
C)1.3 N
D)3.4 × 10^-27 N

Answer 1

3.4 × 10^-25 N

Question 2

The charge in the bottom right corner of the figure is Q =- 45 nC.What is the magnitude of the force on Q?

A)1.9 × 10^-2 N
B)1.4 × 10^-2 N
C)2.6 × 10^-2 N
D)3.5 × 10^-2 N

Answer 2

1.9 × 10^-2 N

Question 3

Three charges of magnitude 3.0  10^-4 C each are located at x = 1.0 m,y = 1.0 m,at s = 0.0 m,y = 0.0 m,and at x = -1.0 m,y = 0.0 m.The one in the middle is negative,while the other two are positive.What is the net Coulombic force exerted by them on a negative 3.0  10^-5 C charge located at x = 0.0 m,y = 2.0 m? (The value of k is 9.0 × 10⁹ N·m²/C². )

A)87 N attractive
B)87 N repulsive
C)120 N attractive
D)120 N repulsive

Answer 3

87 N attractive

Question 4

A metal sphere is insulated electrically and is given a charge.If 25 electrons are added to the sphere in giving a charge,how many Coulombs are added to the sphere?

A)- 4.0 × 10-18 C
B)- 4.0 × 10-20 C
C)- 40 C
D)- 25 C

Question 5

The charge at the bottom of the figure is Q = + 17 nC.What is the magnitude of the force on the charge Q?

A)1.9 × 10^-4 N
B)1.2 × 10^-4 N
C)1.6 × 10^-4 N
D)2.3 × 10^-4 N

Question 6

An asteroid has acquired a net charge of 105 C from being bombarded by the solar wind over the years,and is currently in equilibrium whereby it expels electrons at the same rate as it acquires them.How many more electrons does it have than protons?

A)6.56 × 10²⁰
B)656
C)630
D)1.05 × 10^-17

Question 7

An asteroid of mass 58,000 kg carrying a negative charge of 15.0 μC is 180 m from a second asteroid of mass 52,000 kg carrying a negative charge of 11.0 μC .What is the net force the asteroids exert upon each other? (G = 6.673 × 10^-11 N·m²/kg² and k = 9.0 × 10⁹ N·m²/C². )

A)0.000040 N
B)0.0062 N
C)570,000 N
D)510,000 N

Question 8

Two like charges of the same magnitude are 5.0 mm apart.If the force of repulsion they exert upon each other is 2.0 N,what is the magnitude of each charge? (The constant of proportionality for the Coulombic force is 9.0 × 10⁹ N·m²/C². )

A)7.5 × 10^-2 C
B)7.5 × 10^-8 C
C)7.2 × 10² C
D)7.5 × 10^-5 C

Question 9

A 3.0 μC positive charge is located at the origin and a 2.0 μC positive charge is located at x = 0.0 m,y = 1.0 m.Find the point between them where the electric field strength is zero.

A)x = 0 m,y = 0.55 m
B)x = 0 m,y = 0.67 m
C)x = 0 m,y = 1.5 m
D)x = 0 m,y = 0.60 m

Question 10

A small glass bead has been charged to 8.0 nC? What is the strength of the electric field 2.0 cm from the center of the bead?

A)1.8 × 10⁵ N/C
B)3.6 × 10³ N/C
C)1.4 × 10^-3 N/C
D)3.6 × 10^-6 N/C

Question 11

Two equally charged spheres of mass 1.0 g are placed 2.0 cm apart.When released,they begin to accelerate at 414 m/s².What is the magnitude of the charge on each sphere?

A)140 nC
B)120 nC
C)95 nC
D)75 nC

Question 12

The electric field 2.8 cm from a small object points toward the object with a strength of 180,000 N/C.What is the object's charge?

A)- 16 nC
B)+ 16 nC
C)- 17 nC
D)+ 17 nC

Question 13

A small piece of aluminum (atomic number 13)contains 1015 atoms.(The atomic number is the number of protons;it determines the (positive)electric charge of the nucleus and,thus,the number of electrons in a neutral atom. )If the piece of aluminum has a net positive charge of 3.0 μC,what fraction of the electrons that the aluminum had when it was neutral would have had to be lost?

A)
B)
C)1.9 × 10^-20
D)1.4 × 10^-21

Question 14

What is the electric field strength at x = 0 m,y = 0 m produced by two electrons,one at x = 0.0001 m,y = 0 m and the other at x = -0.0001 m,y = 0 m? (The value of k is 9.0 × 10⁹ N·m²/C². )

A)0 N/C
B)1.8 × 10^-19 N/C
C)2.88 × 10^-19 N/C
D)5.76 × 10^-19 N/C

Question 15

In the figure Q = 5.8 nC and all other quantities are exact.What is the magnitude of the force on the charge Q?

A)1.8 × 10^-3 N
B)1.0 × 10^-3 N
C)9.0 × 10^-4 N
D)1.2 × 10^-3 N

Question 16

In the figure below the charge in the middle is Q = -3.1 nC.For what charge q1 will charge q2 be in static equilibrium?

A)12 nC
B)6.2 nC
C)3.1 nC
D)25 nC

Question 17

Suppose a van de Graaff generator builds a negative static charge,and a grounded conductor is placed near enough to it so that a 7.0 μC of negative charge arcs to the conductor.Calculate the number of electrons that are transferred.

A)4.38 × 10¹³
B)7.0
C)1.12 × 10^-18
D)43.8

Question 18

A proton is located at x = 1.0 nm,y = 0.0 nm and an electron is located at x = 0.0 nm, y = 4.0 nm.Find the attractive Coulombic force between them.(The value of k is 9.0 × 10⁹ N·m²/C². )

A)1.4 × 10^-11 N
B)5.3 × 10^-18 N
C)5.3 × 10⁸ N
D)5.9 × 10^-15 N

Question 19

What is the magnitude of an electric field that balances the weight of a plastic sphere of mass 6.4 g that has been charged to -3.0 nC?

A)2.1 × 10⁷ N/C
B)2.4 × 10⁶ N/C
C)4.5 × 10⁶ N/C
D)6.4 × 10⁶ N/C

Question 20

What is the strength of an electric field that a 0.010 C negative charge experiences 0.90 mm from a 0.20 C positive charge? (The value of K is 9.0 × 10⁹ N·m²/C². )

A)2.2 × 10¹⁵ N/C
B)5.6 × 10¹⁶ N/C
C)1.1 × 10¹⁵ N/C
D)2.2 × 10¹⁶ N/C

Question 21

When electric field lines are curved,the electric field at any point is tangent to the field line at that point.

Question 22

Three point charges are at the vertices of an equilateral triangle.If the electric field at the midpoint of any side of this triangle points perpendicular to that side away from the inside of the triangle,you can conclude that these three charges have the same amount of charge and are all negative.

Question 23

If one bag contains a charge 8Q and another one contains charge Q,the 8Q-bag exerts 8 times as much force on the Q-bag as the Q-bag exerts on the 8Q-bag.

Question 24

The figure shows two 5.0 g spheres suspended from 1.0-m-long threads.The spheres repel each other after being charged to +91 nC.What is the angle θ?

A)4.1 degrees
B)8.2 degrees
C)12 degrees
D)16 degrees

Question 25

If the electric field strength is 900 N/C at a point 5 cm from an infinite plane of charge,its strength will be reduced to 9 N/C at a point 50 cm from the plane.

Question 26

Two infinite parallel plastic sheets contain equal negative charge densities uniformly spread over their surfaces.The electric field is zero everywhere between these sheets,not just midway between them.

Question 27

The more closely electric field lines are packed together,the stronger the field.

Question 28

It is impossible for any object to have a charge of 7.5 e.

Question 29

Two point charges,Q₁ = -1.0 μC and Q₂ = +3.0 μC,are placed as shown.In the figure,the number of excess electrons in charge Q₁ is closest to:

A)6.3 × 10¹²
B)6.3 × 10¹³
C)2.0 × 10¹¹
D)2.0 × 10¹²
E)2.0 × 10¹³

Question 30

If the electric field strength is 500 N/C at a point 2 cm from an infinite line of charge,the field will be 125 N/C at a point 4 cm from this line.

Question 31

Two nuclei each contain two protons and exert a force 4 N on each other.If we transfer a proton from one of these nuclei to the other,the force on each nucleus is now reduced to 3 N.

Question 32

A point charge Q = -12 μC,and two other charges,q₁ and q₂,are placed as shown.The electric force components on charge Q are F_x = +0.005 N and F_y = -0.003 N.In the figure,the number of excess electrons in charge Q is closest to:

A)5.5 × 10¹³
B)6.5 × 10¹³
C)7.5 × 10¹³
D)8.5 × 10¹³
E)9.5 × 10¹³

Question 33

Two neutral objects cannot attract each other electrically because they have no excess charge.

Question 34

Electric field lines begin on negative charges and end on positive charges.

Question 35

An object with a 5.0 μC charge is accelerating at 0.0050 m/s²due to an electric field.If the object has a mass of 2.0 mg,what is the magnitude of the electric field?

A)2.0 N/C
B)- 2.0 N/C
C)0.0020 N/C
D)- 0.0020 N/C

Question 36

A point charge Q = - 400 nC and two unknown point charges,q₁ and q₂,are placed as shown.The electric field at the origin O,due to charges Q,q₁ and q₂,is equal to zero.In the figure,the number of excess electrons in charge Q,is closest to:

A)2.5 × 10²
B)1.4 × 10²
C)2.9 × 10²
D)-1.4 × 10²
E)-2.5 × 10²

Question 37

If two point charges exert a force of 1 N on each other when they are 3 cm apart,they will exert a force of 1/25 N when they are 15 cm apart.

Question 38

If the electric field strength produced by a point charge is 1000 N/C at 5.0 cm from this charge,the strength will be 25,000 N/C at a point 1.0 cm closer to this charge.

Question 39

A pair of charged conducting plates produces a uniform field of 12,000 N/C,directed to the right,between the plates.The separation of the plates is 40 mm.In the figure,an electron is projected from plate A,directly toward plate B,with an initial velocity of vo = 2.0 × 10⁷ m/s.The velocity of the electron as it strikes plate B is closest to:

A)1.2 × 10⁷ m/s
B)1.5 × 10⁷ m/s
C)1.8 × 10⁷ m/s
D)2.1 × 10⁷ m/s
E)2.4 × 10⁷ m/s

Question 40

Two protons slightly separated from one another form an electric dipole.

Question 41

The electric field at point P due to a point charge Q a distance R away has magnitude E.In order to double the magnitude of the field at P,you could

A)double the charge to 2Q.
B)double the distance to 2R.
C)reduce the distance to R/2.
D)reduce the distance to R/4.
E)double the charge to 2Q and at the same time reduce the distance to R/2.

Question 42

If two macroscopic objects are electrically attracted to each other,

A)both objects must be negatively charged.
B)both objects must be positively charged.
C)one object must be negatively charged and the other object must be positively charged.
D)None of the above statements are absolutely true.

Question 43

Four charged particles (two having a charge +Q and two having a charge -Q)are distributed as shown below.Each charge is equidistant from the origin.In which direction is the net electric field at the point P,which is on the y axis?

A)directly up (in the positive y direction)
B)directly left (negative x direction)
C)upwards,toward the left
D)upwards,toward the right
E)The net field is zero,so there is no direction.

Question 44

Two unequal point charges q1 and q2 are held in place separated from each other.A point charge Q is placed somewhere between them at a point where it remains stationary when released.From this observation,we can conclude that q1 and q2 must either both be positive or both be negative.

Question 45

One charged plastic ball is vertically above another in a test tube as shown.The balls are in equilibrium a distance d apart. If the charge on each ball is doubled,the distance between the balls in the test tube would become

A) d.
B)2d.
C)4d.
D)8d.

Question 46

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?

A)Trajectory W
B)Trajectory X
C)Trajectory Y
D)Trajectory Z

Question 47

The electrical force between two objects depends on

A)the distance between the two objects.
B)the charge of the two objects.
C)the mass of the two objects.
D)All of the above
E)Two of the above

Question 48

Two identical small charged spheres are a certain distance apart,and each initially experiences an electrostatic force of magnitude F due to the other.With time,charge gradually diminishes on both spheres.When each of the spheres has lost half its initial charge,the magnitude of the electrostatic force will be:

A)1/16 F.
B)1/8 F.
C)1/4 F.
D)1/2 F.

Question 49

A hydrogen nucleus,which has a charge e,is situated to the left of a carbon nucleus,which has a charge 6e.Which statement is true?

A)The electrical force experienced by the hydrogen nucleus is to the left,and the magnitude is equal to the force exerted on the carbon nucleus.
B)The electrical force experienced by the hydrogen nucleus is to the left,and the magnitude is greater than the force exerted on the carbon nucleus.
C)The electrical force experienced by the hydrogen nucleus is to the left,and the magnitude is less than the force exerted on the carbon nucleus.
D)The electrical force experienced by the hydrogen nucleus is to the right,and the magnitude is equal to the force exerted on the carbon nucleus.

Question 50

A plastic rod is charged up by rubbing a wool cloth,and brought to an initially neutral metallic sphere.It is allowed to touch the sphere for a few seconds,and then is separated from the sphere by a small distance.After the rod is separated,the rod

A)is repelled by the sphere.
B)is attracted to the sphere.
C)feels no force due to the sphere.

Question 51

Two equal and opposite charges a certain distance apart are called an electric "dipole." A positive test charge +q is placed as shown,equidistant from the two charges. Which diagram below gives the direction of the net force on the test charge?

A)

B)

C)
D)

Question 52

The diagram shows electric field lines arising from two small charged particles P and Q. Consider the following two statements:
i.The charge on P is smaller than the charge on Q.
Ii.The electrostatic force on P is smaller than that on Q.
Which of the above statements are true?

A)Only i
B)Only ii
C)Both i and ii
D)Neither i nor ii

Question 53

X and Y are two uncharged metal spheres on insulating stands,and are in contact with each other.A positively charged rod R is brought close to X as shown in figure 1. Sphere Y is now moved away from X (figure 2). The final charge states of X and Y,respectively,are

A)neutral and neutral.
B)positive and neutral.
C)neutral and positive.
D)negative and positive.

Question 54

Two identically charged balls are a certain distance apart.The vectors in the diagram below show the magnitude and direction of the electrostatic force on each ball. Suppose the charge on the left ball is now doubled (represented by two plus signs).Which diagram below best represents the forces that now act on the two balls?

A)

B)

C)

D)

Question 55

The diagram shows two unequal charges +q and -Q,of opposite sign.Charge Q has greater magnitude than charge q.Point X is midway between the charges. In what section of the line will there be a point where the resultant electric field is zero?

A)VW
B)WX
C)XY
D)YZ

Question 56

A positive charge moving along the x-axis passes a negative charge of equal magnitude moving at the same speed but in the opposite direction.The negative charge is only slightly displaced from the x-axis.A point charge is stationary near,but not on,the x-axis,and has the same x-coordinate as the moving charges at the point where they will be closest to each other.Will the point charge experience an electric field that is greater than or less than the field that would result if there were only one moving charge?

Question 57

Two uncharged metal spheres,#1 and #2,are mounted on insulating support rods.A third metal sphere,carrying a positive charge,is then placed near #2.Now a copper wire is momentarily connected between #1 and #2 and then removed.Finally,sphere #3 is removed.In this final state

A)spheres #1 and #2 are still uncharged.
B)sphere #1 carries positive charge and #2 carries negative charge.
C)sphere #1 carries negative charge and #2 carries positive charge.
D)spheres #1 and #2 both carry positive charge.
E)spheres #1 and #2 both carry negative charge.

Question 58

A positive test charge q is released near a positive fixed charge Q. As q moves away from Q,it will move with

A)constant velocity.
B)constant acceleration.
C)increasing acceleration.
D)decreasing acceleration.

Question 59

If you rub a balloon on your sweater and then press it to a wall,it will often stick there.Why does this happen?

A)Rubbing removes a surface layer of grease,allowing the rubber to come in sufficiently close contact with the wall so that air pressure holds it there.
B)Rubbing the balloon charges it electrostatically,and this charge on the balloon induces an opposite charge on the wall.The attraction between the induced charge and the charge on the balloon holds the balloon to the wall.
C)A wall typically has a net electric charge on it,and rubbing the balloon charges it electrostatically.If the wall happens to have opposite charge to that on the balloon,the balloon will stick.
D)Rubbing the balloon causes moisture to condense on it,and surface tension causes the balloon to stick to the wall.
E)Rubbing the balloon surface causes it to become slightly conducting.When the balloon is touched to the wall,electrons flow from the balloon to the wall.This sets up an electric field that bonds the balloon weakly to the wall.

Question 60

The reaction 8p+ + 6e- → 2p+ violates charge conservation because there are more charges before the reaction than afterwards.