Mastering Physics Chapter 19 Electric Charges and Forces

Homework #1

Due: 11:59pm on Wednesday, July 9, 2014

You will receive no credit for items you complete after the assignment is due. Grading Policy

Item 1

The Charge on Adhesive Tape When adhesive tape is pulled from a dispenser, the detached tape acquires a positive charge and the remaining tape in thedispenser acquires a negative charge.

Part A

If the tape pulled from the dispenser has 0.14 of charge per centimeter, what length of tape must be pulled to transfer 1.91013 electrons to the

remaining tape?

Express your answer using two significant figures.

ANSWER:

Correct

Item 2

Consider the three electric charges, A, B, and C, shown in the figure.

Part A

Rank the charges in order of decreasing magnitude of the net force they experience.

Rank charges from largest to smallest magnitude of the net force they experience. To rank items as equivalent, overlap them.

ANSWER:

N$

= 22 DN

Correct

Item 3

Part A

Given that = 14 and = 16 , find the direction and magnitude of the net electrostatic force exerted on the point charge in the figure.


- N$ DN -

ANSWER:

Correct

Part B

ANSWER:

Correct

Item 4

A point charge = -0.32 is fixed at the origin.

Part A

Where must a proton be placed in order for the electric force acting on it to be exactly opposite to its weight? (Let the axis be vertical and the axis be

horizontal.)

ANSWER:

= 86 /

toward the left

toward the right

- O$

5 4

Correct

Part B


ANSWER:

Correct

Item 5

Part A

Find the direction and magnitude of the net electrostatic force exerted on the point charge in the figure. Let and .


above the

below the

-

-

= 5.3 . LN

-

- N$ DN

ANSWER:

Correct

Part B

Express your answer using three significant figures.

ANSWER:

Correct

Item 6

= 3.3 OFU

/

= 175 counterclockwise from - direction J

-

-

N$ N$

IP Two point charges lie on the 10.7 axis. A charge of 9.2 is at the origin, and a charge of -4.4 is at = 10.7 .

Part A

At what position would a third charge be in equilibrium?


ANSWER:

Correct

Part B

Does your answer to part A depend on whether is positive or negative? Explain.

ANSWER:

Submitted, grade pending

Item 7

Two point charges lie on the axis. A charge of 6.2 is at the origin, and a charge of -9.6 is at . What is the net electric field at (a)

and at (b) ?

Part A

DN N$ N$ 4 DN

4 -

= 35 4 DN

-

3508 Character(s) remaining

No, either way it would still be in equilibrium at 35 cm. F13 - F23 and F23 - F13 both equal zero as Coulomb's law uses the absolute value of the charge. The assignment of positive or negative is arbitrary as long as the relationship between the charges and all other factors remain constant.

4 N$ N$ 4 DN

4 DN 4 DN


ANSWER:

Correct

Part B


ANSWER:

Correct

Item 8

An object with a charge of -4.0 and a mass of 1.7102 experiences an upward electric force, due to a uniform electric field, equal in magnitude to its

weight.

Part A

Find the magnitude of the electric field.


ANSWER:

= 3.0107 /$

= 5.9107 /$

N$ LH

= 4.2104 /$

Correct

Part B

Find the direction of the electric field.

ANSWER:

Correct

Part C

If the electric charge on the object is doubled while its mass remains the same, find the direction and magnitude of its acceleration.


ANSWER:

Correct

Part D

If the electric charge on the object is doubled while its mass remains the same, find the direction and magnitude of its acceleration.

ANSWER:

upward

downward

to the left

to the right

= 9.81 NT

Correct

Item 9

Two point charges of equal magnitude are 8.3 apart. At the midpoint of the line connecting them, their combined electric field has a magnitude of 41 .

Part A

Find the magnitude of the charges.


ANSWER:

Correct

Item 10

Two small plastic balls hang from threads of negligible mass. Each ball has a mass of 0.180 and a charge of magnitude . The balls are attracted to each

other, and the threads attached to the balls make an angle of 20.0 with the vertical, as shown in the figure.

upward

downward

to the left

to the right

DN /$

= 3.9 - Q$

H -

Part A

Find the magnitude of the electric force acting on each ball.

ANSWER:

Correct

Part B

Find the tension in each of the threads.

ANSWER:

= 6.42104 /

= 1.88103 /

Correct

Part C

Find the magnitude of the charge on the balls.

ANSWER:

Correct

Item 11

The table below presents the relative charging due to rubbing - also known as triboelectric charging - for a variety of materials. The more plus signs associatedwith a material, the more readily it gives up electrons. Similarly, the more minus signs for a material, the more readily it acquires electrons.

MaterialRelative charging with rubbing

Rabbit fur ++++++

Glass +++++

Human hair ++++

Nylon +++

Silk ++

Paper +

Cotton -

Wood --

Amber ---

Rubber ----

PVC -----

= 5.48 - O$

Teflon ------

Part A

If you rub a rubber balloon against a cloth surface, it can attract a stream of water. Based on the materials listed in table, is the charge of the rubberballoon more likely to be positive or negative?

ANSWER:

Correct

Part B

Explain.

ANSWER:

Part C

If the charge on the balloon is reversed, will the stream of water deflect toward or away from the balloon?

ANSWER:

positive

negative


Essay answers are limited to about 500 words (3800 characters maximum, including spaces).

(none provided)

Correct

Part D

Explain.

ANSWER:

Item 12

Part A

If rabbit fur is rubbed against glass, what is the sign of the charge each acquires? (Refer to the table.)

MaterialRelative charging with

rubbing

Rabbit fur + + + + + +

Glass + + + + +

Rubber - - - -

ANSWER:

toward

away



(none provided)

Correct

Part B

Explain.

ANSWER:

Part C

Repeat part A for the case of glass and rubber.

ANSWER:

Part D

This question will be shown after you complete previous question(s).

rabbit fur - positive, glass - negative

rabbit fur - negative, glass - positive



(none provided)

rubber - positive, glass - negative

rubber - negative, glass - positive

Part E

Comparing the situations described in parts A and C, in which case is the magnitude of the triboelectric charge the greatest?

ANSWER:

Part F


Item 13

Four pairs of conducting spheres, all with the same radius, are shown in the figure, along with the netcharge placed on them initially. The spheres in each pair are now brought into contact, allowingcharge to transfer between them.

in part (a)

in part (c)

Part A

Rank the pairs of spheres in order of decreasing magnitude of the charge transferred.

Rank from largest to smallest. To rank items as equivalent, overlap them.

ANSWER:

Correct

Item 14

Suppose the charge in the figure can be moved left or right along the line connecting the charges

and .

Part A

Given that , find the distance from where experiences a net electrostatic force of zero. (The charges and are separated by a

fixed distance of 42 .)


ANSWER:

Correct

Item 15

IP The point charges in the figure have the following values: = 2.2 , = 6.3 , = -0.86 .

-

-

-

- N$ -

-

-

-

DN

= 15 4 DN

-

N$ -

N$ -

N$

Part A

Given that the distance in the figure is 4.57 , find the direction and magnitude of the net electrostatic force exerted on the point charge .


ANSWER:

Part B


ANSWER:

Part C

How would your answer to part A change if the distance were doubled?

ANSWER:

Part D


DN -

= OFU

/

= counterclockwise from - direction J

-

-

increased by the factor of 2

increased by the factor of 4

decreased by the factor of 2

decreased by the factor of 4

stay the same

Score Summary:

Your score on this assignment is 97.2%.You received 19.43 out of a possible total of 20 points.

Documents

Mastering Physics Chapter 19 Electric Charges and Forces