Deck 15: Electric Forces and Fields

Question 1

A metallic object holds a charge of −4.8 × 10−⁶ C.What total number of electrons does this represent? (e = 1.6 × 10−¹⁹ C is the magnitude of the electronic charge. )

A)3.0E+13
B)7.8E+13
C)1.9E+13
D)7.8E+14
E)1.6E+14

Answer 1

1.9E+13

Question 2

The charge per unit length on an insulator is 6.2 μC/m.On a 2.0-m length of this material,what is the difference in the number of electrons and the number of protons?

A)There are 7.8 × 10¹³ more electrons than protons.
B)There are 7.8 × 10¹³ more protons than electrons.
C)There are 3.9 × 10¹³ more protons than electrons.
D)There are 3.9 × 10¹³ more electrons than protons.

Answer 2

There are 7.8 × 10¹³ more protons than electrons.

Question 3

When a glass rod is rubbed with silk,which of the following statements best describes what happens?

A)Electrons are removed from the rod.
B)Protons are removed from the silk.
C)The silk is charged positively.
D)The silk remains neutral.

Answer 3

Electrons are removed from the rod.

Question 4

A repelling force must occur between two charged objects under which conditions?

A)Charges are of unlike signs.
B)Charges are of like signs.
C)Charges are of equal magnitude.
D)Charges are of unequal magnitude.

Question 5

When charging two objects by rubbing them together

A)Neither may be a conductor.
B)They must be made of different material.
C)They will sometimes end up with both being positively charged.
D)The heat produced by friction is a necessary part of this process.

Question 6

Which of the following best characterizes electrical insulators?

A)charges on the surface don't move
B)high tensile strength
C)electric charges move freely
D)good heat conductors

Question 7

An uncharged conductor is supported by an insulating stand.I pass a positively charged rod near the left end of the conductor,but do not touch it.The right end of the conductor will be

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

Question 8

About how many electrons are in 40 grams of water (H₂O)?

A)4E+26
B)2E+25
C)1E+24
D)2E+22
E)4E+27

Question 9

If body P,with a positive charge,is placed in contact with body Q (initially uncharged),what will be the nature of the charge left on Q?

A)must be equal in magnitude to that on P
B)must be negative
C)must be positive
D)must be greater in magnitude than that on P

Question 10

Object A has a charge q on it,object B has a charge q on it,and object C has a charge 3q on it.These charges are arranged,one each,at the vertices of an equilateral triangle.Which charge has the greatest magnitude electric force on it?​

A)A
B)B
C)C
D)All have equal magnitude forces on them.
E)​A and B

Question 11

Two small objects are suspended from threads.When the objects are moved close together,they attract one another.Which of the following could produce this result?

A)One object is positively charged and the other is negatively charge.
B)One object is positively charged and the other is uncharged.
C)One object is negatively charged and the other is uncharged.
D)All of the above could result in such attraction.

Question 12

An isolated,charged conductor is in electrostatic equilibrium.Which statement is correct?​

A)​The net charge is never zero inside the conductor.
B)​The electric field is always zero just outside the conductor.
C)​The charge density on the conductor's surface is greatest where the surface is sharpest.
D)​None of these statements are correct.

Question 13

I wish to use a positively charged rod to charge a ball by induction.Which statement is correct?

A)The charge on the ball will be positive.
B)The ball must be a conductor.
C)The ball must be an insulator that is connected temporarily to the ground.
D)The ball is charged as the area of contact between the two increases.

Question 14

Who was the first to determine the electron's charge?

A)Franklin
B)Coulomb
C)Millikan
D)Faraday

Question 15

Doug rubs a piece of fur on a hard rubber rod,giving the rod a negative charge.What happens?

A)Protons are removed from the rod.
B)Electrons are added to the rod.
C)The fur is also charged negatively.
D)The fur is left neutral.

Question 16

Which of the following best characterizes electrical conductors?

A)low mass density
B)high tensile strength
C)electric charges move freely
D)poor heat conductors

Question 17

Of the following substances,which one contains the highest density of free electrons?

A)hard rubber
B)iron
C)amber
D)glass

Question 18

If a negative charge is placed inside a hollow isolated conductor that is originally neutral and the charge does not touch that conductor at any time:

A)both the inner and outer surfaces will become negative.
B)both the inner and outer surfaces will remain neutral.
C)the outside surface of the conductor will become positively charged.
D)the inside surface of the conductor will become positively charged.

Question 19

If body M,with a positive charge,is used to charge body N by induction,what will be the nature of the charge left on the latter?

A)must be equal in magnitude to that on M
B)must be negative
C)must be positive
D)must be greater in magnitude than that on M

Question 20

How can a charged object attract an uncharged object made of non-conducting material?

A)The uncharged object must somehow gain a like charge.
B)The uncharged object must somehow gain an unlike charge.
C)The charges in the uncharged object can become polarized.
D)Attraction of an insulator is not possible.

Question 21

Five equal negative charges are uniformly spaced in a semicircular arc of radius r₀ with its center at the origin.The charges positions in polar coordinates are given by (r₀,θ​_i),where the values of θ​_i are 0°,45°,90°,135°,and 180°.At the position (x,y)= (r₀,-r₀)in the 4th quadrant,which statement best describes the direction of the resulting electric field?

A)The direction is that of a 4th quadrant angle.
B)The direction is that of a 3rd quadrant angle.
C)The direction is that of a 1st quadrant angle.
D)The direction is that of a 2nd quadrant angle.

Question 22

An electron is sent at high speed toward a gold nucleus (charge +79e).What is the electrical force acting on the electron when it is 1.7 × 10−¹⁴ m away from the gold nucleus? (e = 1.6 × 10−¹⁹ C,k_e = 8.99 × 10⁹ N·m²/C²)​

A)6.3E+1 N
B)1.1E-12 N
C)5.0E+3 N
D)6.7E+6 N
E)​8.0E-5 N

Question 23

A 6.6-μC charge is placed at the origin and a second charge is placed on the x-axis at x = 0.1 m.If the resulting force on the second charge is 5.7 N in the positive x-direction,what is the value of its charge?​

A)1.0 μC
B)1.0 nC
C)-1.0 μC
D)-1.0 nC
E)​0 μC

Question 24

An electron with a charge value of 1.6 × 10−¹⁹ C is moving in the presence of an electric field of 400 N/C.What force does the electron experience?

A)8.0E-21 N
B)6.4E-22 N
C)6.4E-17 N
D)4.0E+17 N
E)1.6E-17 N

Question 25

The electric field of a point charge has an inverse ________ behavior.

A)r^1/2
B)r
C)r²
D)r³

Question 26

Two point charges each have a value of 35.5 mC and are separated by a distance of 4.0 cm.What is the electric field midway between the two charges? (k_e = 8.99 × 10⁹ N·m²/C²)​

A)7.1E+8 N/C
B)3.5E+8 N/C
C)1.8E+8 N/C
D)zero
E)​2.0E+8 N/C

Question 27

Charge A and charge B are 3.00 m apart,and charge A is +1.44 C and charge B is +3.10 C.Charge C is located between them at a certain point and the force on charge C is zero.How far from charge A is charge C?​

A)1.78 m
B)2.15 m
C)1.22 m
D)0.465 m
E)2.04 m

Question 28

If the size of the charge value is tripled for both of two point charges maintained at a constant separation,the mutual force between them will be changed by what factor?

A)9
B)3
C)1/3
D)1/9
E)​1

Question 29

Two equal charges,each Q,are separated by some distance.What third charge would need to be placed half way between the two charges so that the net force on each charge would be zero?

A)−Q
B)−Q/2
C)−Q/4
D)−Q/8

Question 30

A 7.0-μC charge is placed at the origin and a second charge is placed on the x-axis at x = 0.3 m.If the resulting force on the second charge is 6.9 N in the positive x-direction,what is the force on the charge at the origin?​

A)6.9 N in the positive x-direction
B)6.9 N in the negative x-direction
C)0 N
D)not able to be determined until the second charge is known
E)​6.9 N in the negative y-direction

Question 31

​A charged particle with mass m is suspended in the air by an upward-directed electric field E.What is the charge on the dust particle?

A)​q = mgE
B)​q = mg/E
C)​q = E/mg
D)​​q = Em​/​g

Question 32

Two point charges,one q and the other -q,form a dipole separated by a distance 2L.A third charge Q is placed midway between these two charges.If the only charge that is negative is -q,what is the force on Q?

A) toward -q
B) toward q
C) toward -​q
D) toward q

Question 33

If the distance between two point charges is doubled,the mutual force between them will be changed by what factor?

A)4
B)2
C)1/2
D)1/4
E)​1

Question 34

Four charges are at the corners of a square,with B and C on opposite
Corners.Charges A and D,on the other two corners,have equal charge,while both B and C have a charge of +1.0 C.What is the charge on A so that the force on B is zero?

A)−1.0 C
B)−0.50 C
C)−0.35 C
D)−0.71 C

Question 35

Electric field is dimensionally equivalent to which of the following?

A)N⋅m/C
B)N/C
C)N⋅m²/C²
D)N/C²

Question 36

Two electrons are separated by 7.0 cm.What is the ratio of the electric force to the gravitational force between them? (m_e = 9.11 × 10−³¹ kg,k_e = 8.99 × 10⁹ N⋅m²/C²,G = 6.67 × 10^-11 N⋅m²/kg²,and e = 1.6 × 10−¹⁹ C)​

A)2.3E+2
B)1.3E+20
C)3.1E+22
D)4.2E+42
E)1

Question 37

Two point charges are 12 cm apart.They are moved to a new separation of 3 cm.By what factor does the resulting mutual force between them change?

A)1/4
B)4
C)1/16
D)16
E)​4.5

Question 38

The constant k_e,which appears in Coulomb's law formula,is equivalent dimensionally to which of the following?

A)N⋅m/C
B)N/C
C)N⋅m²/C²
D)N/C²

Question 39

Two point charges are separated by 12.0 cm and have charges of +5.0 µC and −5.0 µC,respectively.What is the electric field at a point midway between the two charges? (k_e = 8.99 × 10⁹ N·m²/C²)

A)3.7 × 10⁶ N/C
B)2.5 × 10⁷ N/C
C)3.1 × 10⁶ N/C
D)​2.1 × 10⁸ N/C
E)​zero

Question 40

In a thundercloud there may be an electric charge of +30 C near the top of the cloud and −30 C near the bottom of the cloud.These charges are separated by about 4.00 km.What is the electric force between these two sets of charges? (k_e = 8.99 × 10⁹ N·m²/C²)​

A)5.1E+11 N
B)​1.3E+20 N
C)5.1E+5 N
D)​2.0E+9 N
E)​3.2E+13 N

Question 41

A proton initially moves left to right along the x axis at a speed of 7.0 × 10³ m/s.It moves into an electric field,which points in the negative x direction,and travels a distance of 0.70 m before coming to rest.What acceleration magnitude does the proton experience?​

A)7.0E+3 m/s²
B)3.5E+7 m/s²
C)1.8E+9 m/s²
D)1.4E+12 m/s²
E)2.5E+9 m/s²

Question 42

Two charges,+Q and −Q,are located two meters apart and there is a point along the line that is equidistant from the two charges as indicated.Which vector best represents the direction of the electric field at that point?

A)Vector E_A
B)Vector E_B
C)Vector E_C
D)The electric field at that point is zero.

Question 43

An airplane is flying through a thundercloud at a height of 2 500 m.(This is a very dangerous thing to do because of updrafts,turbulence,and the possibility of electric discharge. )If there is a charge concentration of +42 C at height 4 000 m within the cloud and −42 C at height 500 m,what is the magnitude of the electric field E at the aircraft? (k_e = 8.99 × 10⁹ N·m²/C²)

A)9.4E+4 N/C
B)1.7E+5 N/C
C)6.2E+4 N/C
D)2.6E+5 N/C
E)​1.9E+5 N/C

Question 44

A proton moving at 3.0 × 10⁴ m/s is projected at an angle of 30° above a horizontal plane.If an electric field of 400 N/C is acting down,how long does it take the proton to return to the horizontal plane? (Hint: Ignore gravity.m_proton = 1.67 × 10−²⁷ kg,q_proton = 1.6 × 10−¹⁹ C)

A)7.8 × 10−⁷ s
B)1.7 × 10−⁶ s
C)3.9 × 10−⁶ s
D)7.8 × 10−⁶ s

Question 45

Charges of 3.5 µC and −7.6 µC are placed at two corners of an equilateral triangle with sides of 0.1 m.At the third corner,what is the electric field magnitude created by these two charges? (k_e = 8.99 × 10⁹ N·m²/C²)​

A)1.2E+7 N/C
B)3.0E+6 N/C
C)5.5E+6 N/C
D)5.9E+6 N/C
E)​7.9E+6 N/C

Question 46

In x-ray machines,electrons are subjected to electric fields as great as 6.0 × 10⁵ N/C.Find an electron's acceleration in this field.(m_e = 9.11 × 10−³¹ kg,e = 1.6 × 10−¹⁹ C)

A)1.1E+17 m/s²
B)3.4E+13 m/s²
C)8.7E+10 m/s²
D)2.9E+8 m/s²
E)​4.1E+13 m/s²

Question 47

The average distance of the electron from the proton in the hydrogen atom is 0.65 × 10−¹⁰ m.What is the electric field from the proton's charge at the location of the electron? (k_e = 8.99 × 10⁹ N⋅m²/C²,e = 1.6 × 10−¹⁹ C)​

A)3.4E+11 N/C
B)5.4E+6 N/C
C)5.2E+1 N/C
D)2.2E-8 N/C
E)​1.0E-8 N/C

Question 48

A proton initially moves left to right long the x axis at a speed of 9.0 × 10³ m/s.It moves into an electric field,which points in the negative x direction,and travels a distance of 0.8 m before coming to rest.If the proton's mass and charge are 1.67 × 10−²⁷ kg and 1.60 × 10−¹⁹ C respectively,what is the magnitude of the electric field?​

A)4.3E+1 N/C
B)5.3E-2 N/C
C)5.3E-1 N/C
D)6.6E-1 N/C
E)1.1E+0 N/C

Question 49

Two point charges are placed along a horizontal axis with the following values and positions: +3.8 µC at x = 0 cm and −7.6 µC at x = 20 cm.At what point along the x axis is the electric field zero?​

A)10 cm
B)8 cm
C)-5 cm
D)-48 cm
E)​-68 cm

Question 50

Charges q,q,and -q are placed on the x-axis at x = 0,x = 4 m,and x = 6 m,respectively.At which of the following points does the electric field have the greatest magnitude?​

A)x = 3 m
B)x = 5 m
C)x = 8 m
D)The electric field has the same magnitude at all three positions.
E)​x = 7 m

Question 51

A ring of charge of radius r₀ lies in the x-y plane with its center at the origin.The charge counterclockwise from θ = 0º to θ = 180º is uniformly distributed with the total charge equaling Q.The charge counterclockwise from θ = 180º to θ = 360º is uniformly distributed with the total charge for this half of the ring equaling -Q.What is the direction of the electric field on the z-axis at the position (x,y,z)= (0,0,​r₀)?

A)It is in the +y direction.
B)It is in the -z direction.
C)It is in the -​y direction.
D)It has no direction since there.

Question 52

Two point charges,separated by 1.7 cm,have charge values of +2.0 and −4.0 µC,respectively.Suppose we determine that 50 field lines radiate out from the +2.0-µC charge.If so,what might be inferred about the −4.0-μC charge with respect to field lines?​

A)25 radiate out
B)100 radiate out
C)100 radiate in
D)50 radiate in
E)50 radiate out

Question 53

An electron with a speed of 2.0 × 10⁶ m/s moves into a uniform electric field of 550 N/C that is parallel to the electron's motion.How long does it take to bring the electron to rest? (me = 9.11 × 10−³¹ kg,e = 1.6 × 10−¹⁹ C)

A)2.1E-8 s
B)6.4E-9 s
C)1.6E-6 s
D)1.6E-6 s.
E)​3.1E-7 s

Question 54

The electric field in a cathode ray tube is supposed to accelerate electrons from 0 to 3.2 × 10⁷ m/s in a distance of 2.00 cm.What electric field is required? (m_e = 9.11 × 10−³¹ kg and e = 1.60 × 10−¹⁹ C)​

A)4.6E+4 N/C
B)2.3E+5 N/C
C)1.5E+5 N/C
D)2.9E+5 N/C
E)1.6E+4 N/C

Question 55

The number of electric field lines passing through a unit cross-sectional area is indicative of

A)field direction.
B)charge density.
C)field strength.
D)charge motion.

Question 56

Charge A has 10 electric field lines coming out,Charge B has 20 lines coming out,and Charge C has 30 lines coming in.Which pair of these charges will have the largest force between them if placed one cm apart?

A)A and B
B)B and C
C)C and A
D)More information is needed.

Question 57

Three equal positive charges are placed on the x-axis,one at the origin,one at x = 4 m,and the third at x = 7 m.Of the following points,which has the greatest magnitude electric field?​

A)x = 3 m
B)x = 5.5 m
C)x = 8 m
D)The electric field has the same magnitude at all three positions.
E)​x = 0 m

Question 58

Electrons in a particle beam each have a kinetic energy of 4.0 × 10−¹⁷ J.What is the magnitude of the electric field that will stop these electrons in a distance of 0.3 m? (e = 1.6 × 10−¹⁹ C)

A)1.9E+3 N/C
B)7.5E+3 N/C
C)8.3E+2 N/C
D)1.3E+3 N/C
E)​6.3E+3 N/C

Question 59

A charge of +2 C is at the origin.When charge Q is placed at 2 m along the positive x axis,the electric field at 2 m along the negative x axis becomes zero.What is the value of Q?

A)−3 C
B)−6 C
C)−7 C
D)−8 C

Question 60

Q₁ has 50 electric field lines radiating outward and Q₂ has 250 field lines converging inward.What is the ratio Q₁/Q₂?​

A)5
B)−5
C)1/5
D)−1/5
E)​0

Question 61

In Millikan's oil drop experiment,if the electric field between the plates was of just the right magnitude,it would exactly balance the weight of the drop.Suppose a tiny spherical oil droplet of radius 1.3 × 10−⁴ cm carries a charge equivalent to one electron.What electric field is required to balance the weight? (The density of oil is 0.85 g/cm³,e = 1.6 × 10−¹⁹ C. )​

A)3.8E+6 N/C
B)6.0E+4 N/C
C)9.4E+2 N/C
D)4.8E+5 N/C
E)1.3E+7 N/C

Question 62

We have an initially uncharged hollow metallic sphere with radius of 5.0 cm.I place a small object with a charge of +20 µC at the center of the sphere through a hole in the surface.Find the electric field present at a point 10 cm from the sphere's center.(k_e = 8.99 × 10⁹ N⋅m²/C²)​

A)3.6E+7 N/C
B)9.0E+6 N/C
C)1.8E+7 N/C
D)4.5E+6 N/C
E)​2.7E+7 N/C

Question 63

If a charge +Q is placed inside a hollow isolated conductor that is originally neutral and the charge does not touch that conductor at any time:

A)the inside surface of the conductor will become positively charged.
B)the outside surface of the conductor will become positively charged.
C)both the inner and outer surfaces will remain neutral.
D)both the inner and outer surfaces will become negative.

Question 64

In the Millikan oil-drop experiment it was found that oil droplets:

A)could only have positive net charge.
B)could only have negative net charge.
C)could only have negative or zero net charge.
D)could have positive,negative,or zero net charge.

Question 65

The Millikan oil-drop experiment demonstrated that:

A)small oil drops fall slowly through the air.
B)light beams can be used to illuminate small oil droplets.
C)the electronic charge is quantized.
D)falling oil droplets reach terminal speed.

Question 66

Relative distribution of charge density on the surface of a conducting solid depends on the

A)shape of the conductor.
B)mass density of the conductor.
C)type of metal of which the conductor is made.
D)strength of the earth's gravitational field.

Question 67

Two identical iron spheres have equal positive charges and the force between them when they are 1 m apart is 2 N.What percentage of the electrons has been removed from each sphere if each sphere has 1 mole (6 × 10²³)of iron atoms? (k_e = 8.99 × 10⁹ N⋅m²/C²,the atomic number of iron is 26,and the electron charge is −1.6 × 10−¹⁹ C)​

A)0.001%
B)0.000 002%
C)1 × 10−⁸ %
D)6 × 10−¹⁰ %
E)​6 × 10−¹² %

Question 68

Two identical balls have the same amount of charge,but the charge on ball A is positive and the charge on ball B is negative.The balls are placed on a smooth,level,frictionless table whose top is an insulator.Which of the following is true?

A)Since the force on A is equal but opposite to the force on B,they will not move.
B)They will move together with constant acceleration.
C)Since the force on both balls is negative,they will move in the negative direction.
D)None of the above is correct.

Question 69

We have a hollow metallic sphere with charge −5.20 µC and radius 5.40 cm.We insert a +10.4-µC charge at the center of the sphere through a hole in the surface.What charge now rests on the outer surface of the sphere?​

A)+5.20 µC
B)+15.6 µC
C)-5.20 µC
D)-15.6 µC
E)​-10.4 µC

Question 70

A ping-pong ball covered with a conducting graphite coating has a mass of 5.4 × 10−³ kg and a charge of 3.8 µC.What electric field directed upward will exactly balance the weight of the ball? (g = 9.8 m/s²)​

A)7.2E+1 N/C
B)1.4E+4 N/C
C)6.3E-8 N/C
D)2.1E+6 N/C
E)6.9E+6 N/C

Question 71

An initially uncharged hollow metallic sphere with radius of 5 cm has a small object with a charge of +15 µC carefully placed at the center of the sphere through a hole in the latter's surface.What charge resides inner surface of the sphere?

A)-2 000 µC
B)-15 µC
C)+15 µC
D)zero
E)​+2 000

Question 72

Two identical spheres each carry a charge of −82.0 µC.The spheres are separated by a distance of 2.00 m.What is the electric force between the spheres? (k_e = 8.99 × 10⁹ N·m²/C²)​

A)0.184 N (repulsive)
B)15.1 N (repulsive)
C)30.2 N (attractive)
D)1.47 N (attractive)
E)​37.8 N (attractive)

Question 73

The electric field at the surface of a positively charged conductor has a direction characterized by which of the following?

A)tangent to the surface
B)perpendicular inward toward the charge
C)at a 45° angle to the surface
D)perpendicular outward and away from the charge

Question 74

An initially uncharged hollow metallic sphere with radius of 6 cm has a small object with a charge of +14 µC carefully placed at the center of the sphere through a hole in the latter's surface.With the charge in place,what charge is now present on the outside surface of the sphere?​

A)zero
B)−14 µC
C)+5 600 µC
D)+14 µC
E)​−5 600 µC

Question 75

The electric field associated with a uniformly charged hollow metallic sphere is the greatest at:

A)the center of the sphere.
B)the sphere's inner surface.
C)infinity.
D)the sphere's outer surface.

Question 76

At what point is the charge per unit area greatest on the surface of an irregularly shaped conducting solid?

A)where surface curves inward
B)where surface is flat
C)where curvature is least
D)where curvature is greatest

Question 77

Two point charges,one ​q and the other -q,form a dipole separated by a distance d.A third charge Q is placed midway between these two charges.If the distance between q and -q is then doubled with the Q staying midway between the other two,what happens to the force on Q?

A)It halves.
B)It reduces by a factor of 8.
C)It stays the same.
D)It quarters.

Question 78

The combination of two separated point charges of opposite sign but equal magnitude is called an electric:

A)monopole.
B)dipole.
C)quadrapole.
D)magnapole.

Question 79

If a conductor is in electrostatic equilibrium near an electrical charge:

A)the total charge on the conductor must be zero.
B)the electric field inside the conductor must be zero.
C)any charges on the conductor must be uniformly distributed.
D)the sum of all forces between the conductor and the charge must be zero.

Question 80

A thin uncharged conducting spherical shell has a charge q carefully placed at its center through a small hole in the shell.The charge q does not touch the shell.What is the charge on the outer surface of the shell?

A)q
B)−q
C)2q
D)0