Questions From Notes
1. Write the word for each of the definitions below.
(a) a device used to detect the presence of a static electric charge
electroscope
.
(b) to discharge an object by connecting it to the ground
grounding
(c) a material that holds charges very tightly
insulator
(d) a material that allows charges to move freely
conductor
2. State 3 methods to charge an object.
friction
contact
induction
3. (a) Which methodes) produce the same charge?
contact
(b) Which methodes) produce a different charge?
friction
induction
4. State 4 ways to discharge a charged object.
grounding
water molecules
shining a light
radiation
5. When you ground a negative object, what happens?
(b) electrons move from the charged object to the ground
6. Use the electrostatic series chart to answer the following questions.
If the following are rubbed together and charged by friction, what charge would each
material take on?
(a) Ebonite Rod
__
__
and
Silk
_+__
(b) Glass Rod
__ +_
and
Fur
_
(c) Glass Rod
__ +_
and
Silk
_
(d) Acetate Strip
__ +_
and
Fur
_
(e) Acetate Strip
__ +_
and
Silk
_
(f) Wool Sweater
__ +_
and
Cotton Shirt
_
7. (a) If you wanted to give a neutral object a positive charge by induction, what type of
charged object would you use, a positively or a negatively charged object? Why?
negatively charged object
Charging by induction produces the opposite charge of the object inducing
the charge.
(b) If you wanted to give a neutral object a positive charge by contact, what type of
charged object would you use, a positively or a negatively charged object? Why?
positively charged object
Charging by contact produces the same charge as the object doing the
charging.
REVIEW QUESTIONS
p.300
1. What is similar about a spark and a lightning bolt?
Sparks are just really small versions of lightning. Both are produced when
an electric discharge occurs through the air in the space between two
oppositely charged objects.
2. How do some charged objects interact with each other differently from the way a
charged object interacts with neutral objects?
Charged objects all seem to attract neutral objects. However, some pairs of
charged objects appear to repel each other, while other pairs of charged
objects attract each other.
6. What do you think would happen if you rubbed two identical objects together?
Would they attract each other, repel each other, or neither attract nor repel each
other? Why?
If two identical objects were rubbed together they should neither attract nor
repel each other. Only two different objects seem to be able to produce the
conditions for static electricity to be observed.
p.306
2. What makes objects neutral?
When an object has the same number of negative charges (electrons) and
positive charges (protons), it is said to be electrically neutral.
5. Explain the difference between a negatively charged object and a positively
charged object.
A negatively charged object has more negative charges distributed through
its molecules. The molecules of a positively charged object contain more
positive charges than negative charges.
p.312
2. What type of charge moves through conductors? Explain how it moves.
Negative charges move through conductors. These negative charges are
electrons. The electrons are able to move from atom to atom through a
conductor, thus allowing a charge to move.
3. What does it mean when you say that a conductor is grounded?
For a conductor to be grounded, it must be connected by another conductor
to a neutral object much larger than the original object. Usually, a grounded
object is connected to Earth.
Practical Applications of Electricity Questions
pp.313-318
1. What is an electrostatic precipitator? What is it used for?
An electrostatic precipitator is a device to control air pollution using stationary
electric charges (not currents).
Exhaust gases enter a cylinder, insulated from the walls made of a grounded
conductor. This central conductor is so highly charged that it causes molecules
(potential pollutants) in the gases to split into ions. These ions initiate electrical
discharges, much like lightning. Each discharge causes more ions to form.
Nearly all particles and liquid droplets in the exhaust gas become ionized. The
charged, central conductor repels the ions and drives them to the outside wall.
Since the outside wall is grounded, it neutralizes the ions when they hit. The
neutralized ions form liquid droplets or solid particles. The liquids run down
the wall and the solids stick to it. Solids can be removed by vibrating the wall or,
if necessary, scraping them off.
2. Explain how electrostatic spray painting works for painting cars.
The car is given a positive charge. As the paint leaves the nozzle of the gun, it
becomes negatively charged and is then attracted to the positive target. This
results in an excellent paint job. The electrostatic paint process increases the
efficiency of paint application by reducing the amount of overspray (paint that
misses the target) thus creates less waste.
3. What is "static cling?"
Static cling refers to the tendency for clothes of different materials to stick
together after they are removed from a tumble dryer. Different clothing
materials rub together in the dryer in much the same way that different
materials were rubbed together in the various activities conducted in the lab.
One clothing item will tend to give up electrons, while the other will tend to
acquire electrons, resulting in the two items acquiring opposite charges.
4. What is a lightning rod?
A lightning rod is a rod made of a conducting material (a metal or wire)
attached to a building to prevent lightning damage by conducting the electrons
to the ground. It provides a low resistance path to allow the electric charge to
get to the ground, thus preventing the building from reaching a temperature
where it would catch fire. Lightning rods may have different shapes, but they all
have a mass of conducting material and a pointed end that reaches upward.
Lightning rods are connected by a conducting pole or cable to a plate or loop of
metal embedded in the soil.
5. What is thunder?
Thunder is the sound produced by a lightning bolt. It is the shock that is created
as super-heated air expands outward from the space around the lightning bolt.
6. Why does a house usually catch fire when lightning hits it?
When the electric charge from the lightning strike tries to travel through the
structure of the house, it encounters a great deal of resistance. This resistance
causes the structure of the building to heat up to the point where the building
will catch fire.
7. One of the safest places to be during a lightning storm is inside a car (with the
windows closed, of course). Why is this so?
Most think that the rubber tires protect the car because rubber is an electrical
insulator. Just a little thought will make you realize that if the lightning can
travel several hundreds of metres from the cloud to the car, the small distance
from the bottom of the car body to the ground is insignificant. The car is a safe
place to be because if lightning strikes a car, the current is distributed across the
entire outer surface of the car (because the car body is usually made of metal
which is a good conductor, and is also often wet from the rain). Lightning does
not tend to move inside the car, unless the windows are open.
pp.320-321
17. You can get a shock after walking across a nylon carpet and touching a metal
doorknob, but not a wooden doorknob. Explain why this is true.
The wooden doorknob is made of an insulating material. The electrons in
such materials are not able to move in response to the large charge on your
hand. Since these electrons cannot set up the large opposite charge required
to ionize the air, a spark, and, therefore, a shock, cannot be produced.
18. Assume you rub a material with fur and the material becomes charged. Explain
how you could use a negative ebonite rod or a positive glass rod to determine the
type of charge on the material.
Suspend the charged material from a stirrup support so it is free to rotate
but is not in contact with the ground. When you approach the charged
material with a negative ebonite rod, if the material is repelled by the
ebonite, then the material is negatively charged. If the material is attracted
by the ebonite, then the material is positively charged. When you approach
the charged material with a positive glass rod, if the material is attracted to
the glass rod, then the material is negatively charged. If the positive glass
rod repels the material, the material is then positively charged.
22. Imagine that you walk into a room where someone has been working with an
electroscope. There is no one there and nothing is near the sphere of the
electroscope but the leaves are spread wide apart. You rub an ebonite rod with
fur. As you slowly bring the rod near the sphere of the electroscope, the leaves
begin to fall back down and lie near each other.
(a) Explain why the leaves of the electroscope were in the condition in which
you found them.
The leaves were far apart because there was either an excess or deficiency of
electrons on the electroscope (in this case there was a deficiency of electrons),
The charge is spread across the electroscope, and since the leaves have a
similar charge, they repel each other and spread apart.
(b) Explain what happened as you brought the ebonite rod near to the sphere
of the electroscope.
Since the leaves were positively charged, the presence of the charged ebonite
rod caused electrons in the sphere of the electroscope to be forced down into
the leaves, thus balancing the positive charge, and temporarily rendering the
leaves neutral.
26. Why are the handles of screwdrivers often made of plastic or rubber?
Both plastic and rubber are insulating materials. Since screwdrivers may get
used for electrical wiring work, it is safer if they are unable to conduct a
potential chare to the person holding the tool.
28. Four pith balls, a, B, C, and D, are suspended on insulating threads. Sphere A, B,
and C attract each other. Ball C repels D. If A is positively charged, what type of
electric charge is on B, C, and D?
A is positive (given); B is neutral (since it attracts both A and C); Cis
p~§i~ (since it attracts A but repels D); D is ~~
(since it repels C).
i'U_,\
(vA
U
29. If a metal marble, resting on insulating material, is given a negative charge, will
the charge be distributed evenly throughout the entire marble or will it all be on
the surface? Use the properties of charge and of conductors to explain why you
chose your answer.
The charge is likely to reside entirely on the surface of the ball. As a
conductor, the charging is free to move anywhere within the structure of the
ball, but each charge wants to be as far from other negative charges as
possible. The charges accomplish this by collecting on the outer surface.
32. Platinum and silver are excellent conductors yet they are rarely used in cornmon
applications. Why?
Platinum and silver are rarely used in common applications because they
are too expensive. Other materials, such as copper and even aluminum
provide the best combination of good conductive properties and reasonable
cost.