Question 1

A point charge Q₁ = +6.0 nC is at the point (0.30 m, 0.00 m); a charge Q₂ = -1.0 nC is at (0.00 m, 0.10 m), and a charge Q₃ = +5.0 nC is at (0.00 m, 0.00 m). What are the magnitude and direction of the net force on the +5.0-nC charge due to the other two charges? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

Accepted Answer

5.4 µN at 56° above -x-axis

Question 2

An asteroid of mass 58,000 kg carrying a negative charge of $15 \mu \mathrm { C }$ is $180 \mathrm {~m}$ from a second asteroid of mass $52,000 \mathrm {~kg}$ carrying a negative charge of $11 \mu \mathrm { C } \text {. }$ What is the magnitude of the net force the asteroids exert upon each other, assuming we can treat them as point particles? (G = 6.67 × 10-11 N ∙ m2/kg2, k = 1/4 πε0 = 8.99 × 109 N ∙ m2/C2)

Accepted Answer

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

Question 3

A point charge Q = -12 μC, and two other charges q₂ and q₂, are placed on x-y axes as shown in the figure. The electric force components on charge Q are F_x = +0.005 N and Fy = -0.003 N. (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C², e = 1.6 × 10^-19C) (a) How many excess electrons are there in charge Q? (b) What are the charges q1 and q2, including their signs?

Accepted Answer

(a) 7.5 × 10¹³ electrons (b) q₁ = +600 nC, q₂ = -640 nC

Question 4

The electric field at a point 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 q? 
(k = 1/4πε0 = 8.99 × 109 N ∙ m2/C2)

Accepted Answer

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

Question 5

An electron is initially moving to the right when it enters a uniform electric field directed upwards, as shown in the figure. Which trajectory (X, Y, Z, or W) will the electron follow in the field?

Accepted Answer

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

Question 6

Two point charges, Q1 and Q2, are separated by a distance R. If the magnitudes of both charges are halved and their separation is also halved, what happens to the electrical force that each charge exerts on the other one?

Accepted Answer

A)   It increases by a factor of 16.
B)   It increases by a factor of 8.
C)   It increases by a factor of 2.
D)   It increases by a factor of 4.
E)   It remains the same.

Question 7

A tiny 0.0250-µg oil drop containing 15 excess electrons is suspended between two horizontally closely-spaced metal plates that carry equal but opposite charges on their facing surfaces. The plates are both circular with a radius of 6.50 cm. (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C², e = 1.6 × 10^-19 C) (a) How much excess charge must be on each plate to hold the oil drop steady? (b) Which plate must be positive, the upper one or the lower one?

Accepted Answer

The answer of A tiny 0.0250-µg oil drop containing 15...

Question 8

Two parallel square metal plates, 8.4 cm on each side, are 2.5 mm apart and carry equal but opposite charge uniformly distributed over their facing surfaces. How much excess charge is there on each plate if the electric field between the plates has a magnitude of 2.0 × 10⁶ N/C? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

Accepted Answer

The answer of Two parallel square metal plates, 8.4 cm...

Question 9

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

Accepted Answer

A)   directly up (in the +y direction) 
B)   directly left (-x direction) 
C)   upwards and towards the left
D)   upwards and towards the right
E)   The net field is zero, so there is no direction.

Question 10

If a point charge of -30 µC experiences an electrostatic upward force of 27 mN at a certain location in the laboratory, what are the magnitude and direction of the electric field at that location?

Accepted Answer

The answer of If a point charge of -30 µC...

Question 11

Which one of the arrows shown in the figure best represents the direction of the electric field between the two uniformly charged metal plates?

Accepted Answer

A)   A
B)   B
C)   C
D)   D
E)   None of the above

Question 12

A small 0.050-kg insulating sphere carries a charge of -60 μC and is hanging by a vertical silk thread from a fixed point in the ceiling. An external uniform vertical electric field is now applied. If the applied electric field has a magnitude of 3000 N/C and is directed downward, what is the tension in the silk thread? (k = 1/4πε0 = 9.0 × 109 N ∙ m2/C2)

Accepted Answer

A)   0.19 N
B)   0.31 N
C)   0.41 N
D)   0.52 N
E)   0.71 N

Question 13

An electron is placed in a uniform electric field of 4.5 × 104 N/C that points to the right. (e = 1.6 × 10^-19 C, m_electron = 9.11 × 10-31 kg) (a) What are the magnitude and direction of the force on the electron? (b) If the electron is released from rest, what is its speed after 3.0 ps?

Accepted Answer

The answer of An electron is placed in a uniform...

Question 14

(a)

(b)

X and Y are two initially uncharged metal spheres on insulating stands, and they are in contact with each other. A positively charged rod R is brought close to X as shown in part (a) of the figure. Sphere Y is now moved away from X, as shown in part (b). What are the final charge states of X and Y?

Accepted Answer

A)   Both X and Y are neutral.
B)   X is positive and Y is neutral.
C)   X is neutral and Y is positive.
D)   X is negative and Y is positive.
E)   Both X and Y are negative.

Question 15

Two electrons are $20.0 \mathrm {~mm}$ apart at closest approach. What is the magnitude of the maximum electric force that they exert on each other? 
(e = 1.60 × 10-19 C, k = 1/4πε0 = 9.0 109 N ∙ m2/C2)

Accepted Answer

A)   5.8 × 10-25 N
B)   2.3 × 1010 N
C)   2.3 N
D)   5.8 × 10-27 N

Question 16

Four point charges of varying magnitude and sign are arranged on the corners of the square of side d as shown in the figure. Which one of the arrows shown represents the net force acting on the point charge with a charge +Q?

Accepted Answer

A)   A
B)   B
C)   C
D)   D

Question 17

A +5.00-μC point charge is placed at the 0.0 cm mark of a meter stick and a -4.00-μC point charge is placed at the 50.0 cm mark. At what point on a line through the ends of the meter stick is the electric field equal to zero?

Accepted Answer

A)   1.4 m from the 0 cm mark
B)   2.5 m from the 0 cm mark
C)   2.9 m from the 0 cm mark
D)   3.3 m from the 0 cm mark
E)   4.7 m from the 0 cm mark

Question 18

Two tiny beads are 25 cm apart with no other charges or fields present. Bead A carries 10 µC of charge and bead B carries 1 µC. Which one of the following statements is true about the magnitudes of the electric forces on these beads?

Accepted Answer

A)   The force on A is 10 times the force on B.
B)   The force on B is 10 times the force on A.
C)   The force on A is exactly equal to the force on B.
D)   The force on A is 100 times the force on B.
E)   The force on B is 100 times the force on A.

Question 19

Two point charges q = -8.50 µC are fixed 10.0 cm apart along a horizontal bar, as shown in the figure. Their electrical forces will be used to balance the weight of a very small sphere carrying a charge $Q = + 15.0 \mu \mathrm { C }$ 10.0 cm from each of them in a place where g = 9.80 m/s2. What is the greatest mass M this sphere can have without falling? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

Accepted Answer

The answer of Two point charges q = -8.50 µC...

Question 20

In outer space, a positive charge q is released near a positive fixed charge Q, as shown in the figure. As q moves away from Q, what is true about the motion of q? (There may be more than one correct choice.)

Accepted Answer

A)   It will move with decreasing speed.
B)   It will move with constant acceleration.
C)   It will move with increasing acceleration.
D)   It will move with decreasing acceleration.
E)   It will move with increasing speed.

Exam 20: Electric Fields and Forces

The electric field at a point 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 q? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

An electron is initially moving to the right when it enters a uniform electric field directed upwards, as shown in the figure. Which trajectory (X, Y, Z, or W) will the electron follow in the field?

Two point charges, Q₁ and Q₂, are separated by a distance R. If the magnitudes of both charges are halved and their separation is also halved, what happens to the electrical force that each charge exerts on the other one?

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

If a point charge of -30 µC experiences an electrostatic upward force of 27 mN at a certain location in the laboratory, what are the magnitude and direction of the electric field at that location?

Which one of the arrows shown in the figure best represents the direction of the electric field between the two uniformly charged metal plates?

An electron is placed in a uniform electric field of 4.5 × 104 N/C that points to the right. (e = 1.6 × 10^-19 C, m_electron = 9.11 × 10-31 kg) (a) What are the magnitude and direction of the force on the electron? (b) If the electron is released from rest, what is its speed after 3.0 ps?

Two electrons are $20.0 \mathrm {~mm}$ apart at closest approach. What is the magnitude of the maximum electric force that they exert on each other? (e = 1.60 × 10^-19 C, k = 1/4πε₀ = 9.0 10⁹ N ∙ m²/C²)

Four point charges of varying magnitude and sign are arranged on the corners of the square of side d as shown in the figure. Which one of the arrows shown represents the net force acting on the point charge with a charge +Q?

A +5.00-μC point charge is placed at the 0.0 cm mark of a meter stick and a -4.00-μC point charge is placed at the 50.0 cm mark. At what point on a line through the ends of the meter stick is the electric field equal to zero?

Two tiny beads are 25 cm apart with no other charges or fields present. Bead A carries 10 µC of charge and bead B carries 1 µC. Which one of the following statements is true about the magnitudes of the electric forces on these beads?

In outer space, a positive charge q is released near a positive fixed charge Q, as shown in the figure. As q moves away from Q, what is true about the motion of q? (There may be more than one correct choice.)

Exam 20: Electric Fields and Forces

The electric field at a point 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 q? (k = 1/4πε0 = 8.99 × 109 N ∙ m2/C2)

An electron is initially moving to the right when it enters a uniform electric field directed upwards, as shown in the figure. Which trajectory (X, Y, Z, or W) will the electron follow in the field?

Two point charges, Q1 and Q2, are separated by a distance R. If the magnitudes of both charges are halved and their separation is also halved, what happens to the electrical force that each charge exerts on the other one?

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

If a point charge of -30 µC experiences an electrostatic upward force of 27 mN at a certain location in the laboratory, what are the magnitude and direction of the electric field at that location?

Which one of the arrows shown in the figure best represents the direction of the electric field between the two uniformly charged metal plates?

An electron is placed in a uniform electric field of 4.5 × 104 N/C that points to the right. (e = 1.6 × 10-19 C, melectron = 9.11 × 10-31 kg) (a) What are the magnitude and direction of the force on the electron? (b) If the electron is released from rest, what is its speed after 3.0 ps?

Two electrons are 20.0 mm20.0 \mathrm {~mm}20.0 mm apart at closest approach. What is the magnitude of the maximum electric force that they exert on each other? (e = 1.60 × 10-19 C, k = 1/4πε0 = 9.0 109 N ∙ m2/C2)

Four point charges of varying magnitude and sign are arranged on the corners of the square of side d as shown in the figure. Which one of the arrows shown represents the net force acting on the point charge with a charge +Q?

A +5.00-μC point charge is placed at the 0.0 cm mark of a meter stick and a -4.00-μC point charge is placed at the 50.0 cm mark. At what point on a line through the ends of the meter stick is the electric field equal to zero?

Two tiny beads are 25 cm apart with no other charges or fields present. Bead A carries 10 µC of charge and bead B carries 1 µC. Which one of the following statements is true about the magnitudes of the electric forces on these beads?

In outer space, a positive charge q is released near a positive fixed charge Q, as shown in the figure. As q moves away from Q, what is true about the motion of q? (There may be more than one correct choice.)

The electric field at a point 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 q? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

Two point charges, Q₁ and Q₂, are separated by a distance R. If the magnitudes of both charges are halved and their separation is also halved, what happens to the electrical force that each charge exerts on the other one?

An electron is placed in a uniform electric field of 4.5 × 104 N/C that points to the right. (e = 1.6 × 10^-19 C, m_electron = 9.11 × 10-31 kg) (a) What are the magnitude and direction of the force on the electron? (b) If the electron is released from rest, what is its speed after 3.0 ps?

Two electrons are $20.0 \mathrm {~mm}$ apart at closest approach. What is the magnitude of the maximum electric force that they exert on each other? (e = 1.60 × 10^-19 C, k = 1/4πε₀ = 9.0 10⁹ N ∙ m²/C²)