Exam (elaborations)
Physics for Scientists & Engineers with Modern Physics (Volume 2) 5e (Global Edition) By Douglas C. Giancoli
Physics for Scientists & Engineers with Modern Physics (Volume 2) 5e (Global Edition) By Douglas C. Giancoli
[Show more]
Connected book
Book Title:
Author(s):
- Edition:
- ISBN:
- Edition:
Content preview
Physics for Scientists & Engineersl l l l
with Modern Physics (Volume 2) 5e
l l l l l l
(Global Edition) By Douglas C.
l l l l l
Giancoli (Solutions Manual All
l l l l
Chapters, 100% Original Verified,
l l l l
A+Grade) l l
(Chapters 21-35) l
All Chapters Solutions Manual
l l l
Supplementfilesdownloadlinkat
l l l l l
theendofthisfile.
l l l l l
(Chapter Number 32 Is Missing) l l l l
,CHAPTER 21: Electric Charge and Electric Field l l l l l l
Responses to Questions l l
1. Suspend a plastic ruler by a thread and then rub it with a cloth. As shown in Fig. 21–2a, the ruler is
l l l l l l l l l l l l l l l l l l l l l
negatively charged. Now bring the charged comb close to the ruler. If the ruler is repelled by the comb,
l l l l l l l l l l l l l l l l l l l
then the comb is negatively charged. If the ruler is attracted by the comb, then the comb is positively
l l l l l l l l l l l l l l l l l l l
charged.
l
2. The shirt or blouse becomes charged as a result of being tossed about in the dryer and rubbing
l l l l l l l l l l l l l l l l l
against the dryer sides and other clothes. When you put on the charged object (shirt), it causes
l l l l l l l l l l l l l l l l l
charge separation within the molecules of your skin (see Fig. 21–9), which results in attraction
l l l l l l l l l l l l l l l
between the shirt and your skin.
l l l l l l
3. Fog or rain droplets tend to form around ions because water is a polar molecule, with a positive region
l l l l l l l l l l l l l l l l l l
and a negative region. The charge centers on the water molecule will be attracted to the ionsor
l l l l l l l l l l l l l l l l l l
electrons, since opposite charges attract.
l l l l l
4. See also Fig. 21–9 in the text. The negatively
l l l l l l l l
charged electrons in the paper are attracted to
l l l l l l l l
the positively charged rod and move towards it
l l l l l l l l
within their molecules. The attraction occurs
l l l l l l
because the negative charges in the paper are
l l l l l l l l
closer to the positive rod than are the positive
l l l l l l l l l
charges in the paper, and therefore the attraction
l l l l l l l l
between the unlike charges is
l l l l l
greater than the repulsion between the like charges.
l l l l l l l
5. A plastic ruler that has been rubbed with a cloth is charged. When brought near small pieces of paper, it
l l l l l l l l l l l l l l l l l l l
will cause separation of charge (polarization) in the bits of paper, which will cause the paper to be
l l l l l l l l l l l l l l l l l l
attracted to the ruler. A small amount of charge is able to create enough electric force tobe stronger than
l l l l l l l l l l l l l l l l l l l l
gravity. Thus the paper can be lifted.
l ll l l l l l
On a humid day this is more difficult because the water molecules in the air are polar. Those polarwater
l l l l l l l l l l l l l l l l l l l
molecules will be attracted to the ruler and to the separated charge on the bits of paper, partially
l l l l l l l l l l l l l l l l l l
neutralizing the charges and thus reducing the attraction.
l l l l l l l l
6. The net charge on a conductor is the sum of all of the positive and negative charges in the conductor.If a
l l l l l l l l l l l l l l l l l l l l l
neutral conductor has extra electrons added to it, then the net charge is negative. If a neutral conductor
l l l l l l l l l l l l l l l l l l
has electrons removed from it, then the net charge is positive. If a neutral conductor has the same amount
l l l l l l l l l l l l l l l l l l l
of positive and negative charge, then the net charge is zero.
l l l l l l l l l l l
The “free charges” in a conductor are electrons that can move about freely within the material
l l l l l l l l l l l l l l l
because they are only loosely bound to their atoms. The “free electrons” are also referred to as
l l l l l l l l l l l l l l l l l
“conduction electrons.” A conductor may have a zero net charge but still have substantial free
l l l l l l l l l l l l l l l
charges.
l
,Chapter 21 Electric Charge and Electric Field
7. Most of the electrons are strongly bound to nuclei in the metal ions. Only a few electrons per atom
l l l l l l l l l l l l l l l l l l
(usually one or two) are free to move about throughout the metal. These are called the “conduction
l l l l l l l l l l l l l l l l l
electrons.” The rest are bound more tightly to the nucleus and are not free to move. Furthermore, inthe
l l l l l l l l l l l l l l l l l l l
cases shown in Figs. 21–7 and 21–8, not all of the conduction electrons will move. In Fig. 21–7,
l l l l l l l l l l l l l l l l l l
electrons will move until the attractive force on the remaining conduction electrons due to the incoming
l l l l l l l l l l l l l l l l
charged rod is balanced by the repulsive force from electrons that have already gathered atthe left end of
l l l l l l l l l l l l l l l l l l l
the neutral rod. In Fig. 21–8, conduction electrons will be repelled by the incoming rod and will leave
l l l l l l l l l l l l l l l l l l
the stationary rod through the ground connection until the repulsive force on the remaining conduction
l l l l l l l l l l l l l l l
electrons due to the incoming charged rod is balanced by the attractive force from the net positive
l l l l l l l l l l l l l l l l l
charge on the stationary rod.
l l l l l
8. The electroscope leaves are connected together at the top. That connection can be
l l l l l l l l l l l l
modeled as a tension force. The horizontal component of this tension force balances
l l l l l l l l l l l l l
the electric force of repulsion. The vertical component of the tension force balances
l l l l l l l l l l l l l
the weight of the leaves.
l l l l l
9. The balloon has been charged. The excess charge on the balloon is able to polarize the water molecules
l l l l l l l l l l l l l l l l l
in the stream of water, similar to Fig. 21–9. This polarization results in a net attraction ofthe water
l l l l l l l l l l l l l l l l l l l
towards the balloon, so the water stream curves towards the balloon.
l l l l l l l l l l l
10. (a) When the leaves are charged by induction, no additional charge is added to the leaves. If the
l l l l l l l l l l l l l l l l l
charged rod is near the top of the electroscope it repels charge onto the leaves causing them to
l l l l l l l l l l l l l l l l l l
separate as in Fig. 21–11(a). When the rod is removed the charge returns to its initial equilibrium
l l l l l l l l l l l l l l l l l
position and the leaves come back together.
l l l l l l l
(b) When the leaves are charged by conduction, positive charge is placed onto the electroscope from
l l l l l l l l l l l l l l
the rod causing the leaves to separate. When the rod is removed, the charge remains on the
l l l l l l l l l l l l l l l l l
electroscope and the leaves remain separated. If not all of the excess charge leaves the rod,then
l l l l l l l l l l l l l l l l l
when the rod is removed, the leaves might come back together slightly from their maximum
l l l l l l l l l l l l l l l
deflection. l
(c) Yes. The electroscope has a negative charge on the top sphere and on the leaves. Therefore the
l l l l l l l l l l l l l l l l
electroscope has a total net negative charge, so it must have been charged by conduction.
l l l l l l l l l l l l l l l
11. Coulomb’s law and Newton’s law are very similar in form. When expressed in SI units, the magnitude
l l l l l l l l l l l l l l l l
of the constant in Newton’s law is very small, while the magnitude of the constant in Coulomb’s law is
l l l l l l l l l l l l l l l l l l l
quite large. Newton’s law says the gravitational force is proportional to the product of the two masses,
l l l l l l l l l l l l l l l l l
while Coulomb’s law says the electrical force is proportional to the product of the two charges.
l l l l l l l l l l l l l l l l
Newton’s law only produces attractive forces, since there is only one kind of gravitational mass.
l l l l l l l l l l l l l l l
Coulomb’s law produces both attractive and repulsive forces, since thereare two kinds of electrical
l l l l l l l l l l l l l l l
charge.
l
12. The gravitational force between everyday objects on the surface of the Earth is extremely small.
l l l l l l l l l l l l l l
(Recall the value of G: 6.6710−11 N m2 kg2 .) Consider two objects sitting on the floor near each
l l l l l l
l
l
lll l l
l l l l l l l l l l
other. They are attracted to each other, but the maximum force of static friction for each is much greater
l l l l l l l l l l l l l l l l l l
than the gravitational force each experiences from the other, and so they don’t move. Even inan
l l l l l l l l l l l l l l l l l
absolutely frictionless environment, the acceleration resulting from the gravitational force would be so
l l l l l l l l l l l l l
small that it would not be noticeable in a short time frame. We are aware of the gravitational force
l l l l l l l l l l l l l l l l l l l
between objects if at least one of them is very massive, as in the case of the Earth and satellitesor the
l l l l l l l l l l l l l l l l l l l l l l
Earth and you.
l l l
, Physics for Scientists & Engineers with Modern Physics, 5e, Global Edition Instructor Solutions Manual
The electric force between two objects is typically zero or very close to zero because ordinary objects
l l l l l l l l l l l l l l l l
are typically neutral or very close to neutral. We are aware of electric forces between objectswhen the
l l l l l l l l l l l l l l l l l l
objects are charged. An example is the electrostatic force (static cling) between pieces of clothing when
l l l l l l l l l l l l l l l l
you pull the clothes out of the dryer.
l l l l l l l l
13. Coulomb observed experimentally that the force between two charged objects is directly proportional to
l l l l l l l l l l l l l
the charge on each one. For example, if the charge on either object is tripled, then theforce is tripled. This
l l l l l l l l l l l l l l l l l l l l l
is not in agreement with a force that is proportional to the sum of the charges instead of to the product of
l l l l l l l l l l l l l l l l l l l l l l
the charges. Secondly, if two equal but opposite charges are placed near to each other, they produce an
l l l l l l l l l l l l l l l l l l
attractive force. But the “sum” version would say the net force is 0 insuch a case. Also, a charged object
l l l l l l l l l l l l l l l l l l l l l
is not attracted to or repelled from a neutral insulating object. If the numerator in Coulomb’s law were
l l l l l l l l l l l l l l l l l l
proportional to the sum of the charges, then there would be a force between a neutral object and a
l l l l l l l l l l l l l l l l l l l
charged object, because the their total charge would not be 0.
l l l l l l l l l l l
14. Assume that the charged plastic ruler has a negative charge residing on its surface. That charge
l l l l l l l l l l l l l l l
polarizes the charge in the neutral paper, producing a net attractive force. When the piece of paperthen
l l l l l l l l l l l l l l l l l l
touches the ruler, the paper can get charged by contact with the ruler, gaining a net negative charge.
l l l l l l l l l l l l l l l l l l
Then, since like charges repel, the paper is repelled by the comb.
l l l l l l l l l l l l
15. The test charge creates its own electric field. The measured electric field is the sum of the original electric
l l l l l l l l l l l l l l l l l l
field plus the field of the test charge. By making the test charge small, the field that it causes is small.
l l l l l l l l l l l l l l l l l l l l l
Therefore the actual measured electric field is not much different than the original field. Also, if the test
l l l l l l l l l l l l l l l l l l
charges are large, their fields might significantly re-distribute the charges causing theoriginal field, and
l l l l l l l l l l l l l l l
then the measurement would not represent the field of the original configuration ofcharges.
l l l l l l l l l l l l l l
16. When determining an electric field, it is best, but not required, to use a positive test charge. A negative
l l l l l l l l l l l l l l l l l l
test charge would be fine for determining the magnitude of the field. But the direction of theelectrostatic
l l l l l l l l l l l l l l l l l l
force on a negative test charge will be opposite to the direction of the electric field. The electrostatic
l l l l l l l l l l l l l l l l l l
force on a positive test charge will be in the same direction as the electric field. In order to avoid
l l l l l l l l l l l l l l l l l l l l
confusion, it is better to use a positive test charge. If we used a negative test charge but
l l l l l l l l l l l l l l l l l l
wanted to have the same result for the electric field, we would have to define E = −F q, q 0.
l l l l l l l l l l l l l l l l l l l l l l
17. See Fig. 21–35(b). A diagram of the electric field lines around two negative charges would be just like
l l l l l l l l l l l l l l l l l
this diagram except that the arrows on the field lines would point towards the charges instead ofaway
l l l l l l l l l l l l l l l l l l
from them. The distance between the charges is l.
l l l l l l l l l
l
18. The electric field will be strongest to the right of the positive charge (between the two charges) and
l l l l l l l l l l l l l l l l l
weakest to the left of the positive charge. To the right of the positive charge, the contributions to thefield
l l l l l l l l l l l l l l l l l l l l
from the two charges point in exactly the same direction, and therefore add. To the left of the positive
l l l l l l l l l l l l l l l l l l l
charge, the contributions to the field from the two charges point in exactly opposite directions, and
l l l l l l l l l l l l l l l l
therefore subtract. Note that this should be confirmed by the density of field lines in Fig. 21–35a.
l l l l l l l l l l l l l l l l l
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller WhiteHouseTutor. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $18.49. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
67479 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 15 years now
