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Current Score:
0/20
Due:
Tue Jan 26 2010 10:15 PM EST
Question
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Description
This assignment is worth 20 points. Each part is worth 1 point.
Assume the numbers given in each problem are accurate to three significant figures. WebAssign expects your answers to be
accurate within 1%. If you don't round off until the end, and then round off to three significant figures, you should be fine.
Occasionally there are errors in WebAssign. If you are convinced your answer is correct and WebAssign is grading you incorrectly
please check with Professor Duffy.
1.
0/1 pointsDuffy_EP_Ch16_P107 [1268003]
Try this at home. Note that you can use a variety of different materials - you don't have to use the materials mentioned below.
A thin stream of water makes an excellent charge detector. By rubbing a balloon on your hair, you give the balloon a negative charge.
Bringing the charged balloon close to the water stream, you observe that the water stream is deflected - the negatively charged
balloon attracts the water.
You then rub a small drinking glass with your silk pajamas - this gives the glass a positive charge. After having removed the balloon,
you bring the glass close to the stream of water. What does the water do?
The water is not deflected at all.
water is repelled by the glass.
water is attracted to the glass.
2.
The
The
0/3 pointsDuffy_EP_Ch16_P02_alternate [1266592]
You have three identical metal spheres that have different initial net charges. Sphere A has a net charge of +3Q; sphere B has a net
charge of -4Q; and sphere C has a net charge of +7Q. You first touch sphere B to sphere A, and then separate them; you then touch
sphere B to sphere C, and then separate them; and finally you touch sphere A to sphere C, and then separate them.
(a) Assuming no charge is transferred to you, what is the total combined charge on the three spheres at the end of the process?
6 Q
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(b) What is the charge on sphere A at the end of the process?
1.38 Q
(c) What is the charge on sphere B at the end of the process?
3.25 Q
3.
0/2 pointsDuffy_EP_Ch16_P106 [1268002]
You have three charged balls, each of which is placed at a particular location on the x-axis. Ball 1 has a charge of +q, and it is
located at x = 0. Ball 2 also has a charge of +q, and it is located at x = -a. Ball 3 has a charge of +4q, and our goal is to determine
where it is located. We do know that that magnitude of the net force experienced by ball 1, because of the other two balls, is
2kq2/a2.Where is ball 3 located?
It turns out that there are two possible locations for ball 3. The one closer to x = 0 is:
x=
1.15 a
The one farther from x = 0 is:
-2 a
x=
4.
0/2 pointsDuffy_EP_Ch16_P29 [836407]
The figure shows the net force experienced by a positive test charge located at the center of the diagram. The force comes from two
nearby charged balls, one (in red) with a charge of +Q and one (in green) with an unknown charge.
(a) Choose the two correct statements from the list below, about the sign and magnitude of the charge on the second ball. You must
select both of the correct answers, and only the correct answers, to receive credit for this question.
The second ball has a positive charge.
The second ball has a negative charge.
information here to determine the sign of the charge on the second ball.
There is not enough
The magnitude of the charge on the second
ball is less than Q.
The magnitude of the charge on the second ball is equal to Q.
on the second ball is greater than Q.
The magnitude of the charge
(b) If Q = 3.20 microcoulombs, determine the charge (sign and magnitude) on the second ball.
-6.4 microcoulombs
5.
0/3 pointsDuffy_EP_Ch16_P14 [1266620]
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Three charged balls are placed so that each is at a different corner of a square, as shown in the figure above. Balls 1 and 3 each
have positive charges, but the sign of the charge on ball 2 is not shown. The figure also shows the net force acting on each of the
balls - the only forces that matter here are those associated with the interactions between the charges.
(a) Based on the information given in the figure, select all the true statements from the set of statements below.
Ball 2 has a positive charge.
sign of the charge on ball 2.
Ball 2 has a negative charge.
There is not enough information to determine the
The charge on ball 1 is larger than the charge on ball 3.
smaller than the charge on ball 3.
The charge on ball 1 is
The charge on ball 1 is equal to the charge on ball 3.
(b) Rank the balls, from largest to smallest, based on the magnitude of the charge on them. Use only > and/or equal signs in your
ranking, such as 2>1=3.
3>1>2
(c) Determine the ratio of the magnitude of the charge on ball 1 to the magnitude of the charge on ball 2.
2
6.
0/3 pointsDuffy_EP_Ch16_P104 [1266204]
The four cases above all show a ball with a charge of -3q at the top right corner of a square. Then there is either one, two, or three
additional charged balls, each ball located at a different corner of the square.
(a) Rank the cases based on the magnitude of the net electrostatic force experienced by the ball of charge -3q, from largest to
smallest. Use only > or = signs in your answer, such as B>A=D>C.
C>A=B>D -or- C>B=A>D
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For the rest of the problem, use q = 4.70 x 10-6 C, and L = 60.0 cm, as well as k = 9.00 x 109 N m2/C2.
(b) In Case C, calculate the magnitude of the net electrostatic force acting on the ball of charge -3q.
2.34 N
(c) In Case D, calculate the magnitude of the net electrostatic force acting on the ball of charge -3q.
0.686 N
7.
0/2 pointsDuffy_EP_Ch16_P42 [836454]
Five balls, two of charge +q and three of charge –2q, are arranged as shown in the figure. The value of q is 2.80 x 10-6C and the
value of r is 30.0 cm.
Note that, in this question, you are only asked to find the magnitude of the net force in each case, but you should also think about the
direction of the net force.
(a) What is the magnitude of the net electrostatic force on the ball of charge +q that is located at the origin? This is the net force
because of the other four charged balls, which are all located a distance r from the origin.
2.35 N
(b) What is the magnitude of the net electrostatic force on the other ball of charge +q, located on the positive y-axis?
0.716 N
8.
0/4 pointsDuffy_EP_Ch16_P105 [1266218]
During the holidays, you probably saw many stars. The five-pointed star above is a little different, having a ball with a positive charge
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Q at each point. Use Q = 5.70 x 10-6 C, and assume that each ball is a distance of 50.0 cm away from the exact center of the star.
Also, use k = 9.00 x 109 N m2/C2.
(a) If we place a sixth charged ball at the exact center of the star, with a charge of +2Q, what is the magnitude of the net electrostatic
force exerted on it by the five charged balls shown above?
0 N
As shown above, we now replace one of the balls of charge Q (the one that was at the top point of the star) by a ball of charge -3Q.
Once again, we want to know the magnitude of the net electrostatic force exerted on a ball of charge +2Q, located at the exact center
of the star, by the five charged balls shown above. One method to do this is to work out the five individual forces, and add them as
vectors, but we should be able to do less work by trying another method, as outlined in parts (b) and (c).
(b) A simpler method is to make use of the answer to part (a). The second picture above, with the ball of -3Q, can be thought of as
the first picture (the one with five identical charged balls) plus a single charged ball, added at the top point of the star, that has a
charge of
-4 Q (enter a sign and number only).
Another way to ask the above is, what do you add to the first picture to get the second picture?
(c) Looked at from the perspective described in (b), the net force on a ball of charge +2Q, located at the exact center of the star in the
second picture, is the vector sum of the answer to part (a), plus the force exerted on the ball of charge +2Q by the ball that is the
answer to part (b). This gives a net force, acting on a ball of charge +2Q in the exact center of the star, that has a magnitude of
9.36 N
(d) The direction of the net force in part (c) has components that are directed (select all that apply)
up
down
left
right
Assignment Details
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