Q: A smartphone charger delivers charge to the phone, in the form of electrons, at a rate of $$-0.75 C/s. $$How many electrons are delivered to the phone during $$17$$ min of charging?

$$4.8 \times 10$$^{22}$$ electrons

Q: In the diagram for FIGURE P22.42, what is the magnitude and direction of the net force on the $$+1 nC $$charge due to the other two charges?

Magnitude: $$1.8 \times 10$$^{-7}$$ N, direction: -y$ axis

Q: A $$-10 nC $$charge is placed at the location of point $$3 in $$the diagram. What is the net electric field at point $$2$$ due to both charges?

$$E = 3.6 \times 10$$^{5}$$ N/C$$\;\hat{y}$$

Q: Two identical small spheres, each of mass $$m$$ and charge $$q$$, are suspended from a common point by threads of length $$L. $$The spheres repel each other and come to equilibrium with each thread making an angle $$\theta$$ with the vertical. Which equation best describes the equilibrium condition?

$$mg \tan \theta = \dfrac{1}{4\pi \$$epsilon_0$$} \dfrac{q^2$}{(2L \sin \$$theta)^2$$}$$

Question 1

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 $$3Q$$?

Accepted Answer

$$F$$

Question 2

A smartphone charger delivers charge to the phone, in the form of electrons, at a rate of $$-0.75 C/s. $$How many electrons are delivered to the phone during $$17$$ min of charging?

Accepted Answer

$$4.8 	imes 10$$^{22}$$ electrons

Question 3

A plastic rod is rubbed with fur and then brought near an uncharged very light $$(m = 20	ext{mg})$$ dielectric (insulating) ball hanging on an insulating string. The ball is uncharged. Describe what will happen as the rod gets very near the ball and why.

Accepted Answer

The ball will be attracted due to polarization of its charges.

Question 4

You have a lightweight spring whose unstretched length is $$4.0 cm. $$First, you attach one end of the spring to your table and hang a $$1.0 g $$mass from its free end. This stretches it to a length of $$5.2 cm. $$You then detach the mass and attach two small plastic beads to the opposite ends of the spring. Lay the spring on a frictionless table, and give each plastic bead the same charge $$Q. $$Stretch the spring to a length of $$4.3 cm. $$What is the magnitude of the charge in $$C on $$each bead?

Accepted Answer

$$1.0 	imes 10$$^{-6}$$ C

Question 5

A positive point charge $$Q is $$fixed on a very large horizontal frictionless tabletop. A second positive charge $$q is $$released from rest a short distance from $$Q$$ and allowed to move freely. Which statement best describes how $$q$$ will behave after it is released?

Accepted Answer

It will move farther and farther from $$Q$$, but its acceleration will keep decreasing.

Question 6

How many electrons are contained in a charge of $$-1.6 	imes 10$$^{-19}$$ C?

Accepted Answer

$$1$$ electron

Question 7

In the diagram for FIGURE P22.42, what is the magnitude and direction of the net force on the $$+1 nC $$charge due to the other two charges?

Accepted Answer

Magnitude: $$1.8 	imes 10$$^{-7}$$ N, direction: -y$ axis

Question 8

A $$-10 nC $$charge is placed at the location of point $$3 in $$the diagram. What is the net electric field at point $$2$$ due to both charges?

Accepted Answer

$$E = 3.6 	imes 10$$^{5}$$ N/C$$\;\hat{y}$$

Question 9

A $$5.0 g $$ball is given a charge of $$+2.0 \muC $$and placed in a uniform electric field of $$1.0 	imes 10$$^{5}$$ N/C directed upward. What is the acceleration of the ball?

Accepted Answer

$$40 m/s$^2$$ upward

Question 10

A $$10 nC $$charge is located at the origin. What is the electric field at a point $$0.5 m $$away from the charge?

Accepted Answer

$$3.6 	imes 10$$^{5}$$ N/C$

Question 11

Two identical small spheres, each of mass $$m$$ and charge $$q$$, are suspended from a common point by threads of length $$L. $$The spheres repel each other and come to equilibrium with each thread making an angle $$	heta$$ with the vertical. Which equation best describes the equilibrium condition?

Accepted Answer

$$mg 	an 	heta = \dfrac{1}{4\pi \$$epsilon_0$$} \dfrac{q^2$}{(2L \sin \$$theta)^2$$}$$

Question 12

A $$1.0 g $$plastic bead is given a charge of $$-2.0 \muC $$and placed in a downward electric field of $$5.0 	imes 10$$^{4}$$ N/C. What is the net force on the bead?

Accepted Answer

$$0.10 N $$upward

Question 13

Which of the following statements about electric field lines is correct?

Accepted Answer

Electric field lines point away from positive charges and toward negative charges.

Question 14

A $$-10 nC $$charge is placed at the origin. What is the direction of the electric field at a point located at $$(0, 1) m$$?

Accepted Answer

Toward the origin

Question 15

A $$1.0 g $$ball is suspended from a thread and given a charge of $$+1.0 \muC. It is $$placed in a horizontal electric field of $$2.0 	imes 10$$^{4}$$ N/C. What is the angle the thread makes with the vertical?

Accepted Answer

$$11^{\circ}$$

Question 16

Which of the following best describes the force between two point charges $$q_1$$ and $$q_2$$ separated by a distance $$r$$?

Accepted Answer

$$F = \dfrac{q_1$ q_2$}{4\pi \$$epsilon_0$$ r^2$}$$

Question 17

A $$-10 nC $$charge is placed at the origin. What is the magnitude of the electric field at a point $$2.0 m $$away?

Accepted Answer

$$4.5 	imes 10$$^{4}$$ N/C$

Electrostatics: Forces, Fields, and Applications

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