Chapter 22 Physics- Electrostatics
What is a transistor composed of, and what are some of its functions?
A transistor is made of thin layers of semiconducting materials sandwiched together. It can be a switch, an oscillator, or an amplifier.
To say a substance is electrically polarized is to say that its net charge is A. is normally zero with opposite charges on opposite ends. B. either negative or positive, but relatively weak. C. weakly positive in sign. D. None of these. E. weakly negative in sign.
A. is normally zero with opposite charges on opposite ends.
Particle A has twice the charge of nearby particle B. Compared to the force on Particle A, the force on Particle B is A. the same. B. four times as much. C. half as much. D. twice as much. E. none of the above
A. the same
What is meant by saying charge is quantized?
All charged objects have a charge that is an integer multiple of the charge of an electron.
capacitor
An electrical device used to store electrical charge.
A main difference between gravitational and electric forces is that electrical forces A. attract. B. repel or attract. C. obey the inverse-square law. D. act over shorter distances. E. are weaker.
B. repel or attract
Why is there no electric field at the center of a charged spherical metal ball?
Because of mutual repulsion, mobile electrons in the conductor will spread out uniformly over the outer surface of the ball, so the force and the field on a test charge at the center is zero because opposing forces balance in every direction.
The five thousand billion billion (5 × 1021) freely moving electrons in a penny repel one another. Why don't they fly out of the penny?
Because they are still bound to the atoms in the penny
What do electrical and heat conductors have in common? What do electrical and heat insulators have in common?
Both conductors transfer energy from one place to another. Both kinds of insulators limit the transfer of energy. Both electrical and heat energy are measured in joules.
Why do clothes often cling together after tumbling in a clothes dryer?
Clothes become charged when electrons from a garment of one material are rubbed onto another material. If the materials were good conductors, discharge between materials would soon occur. But the clothes are non-conducting and the charge remains long enough for oppositely charged garments to be electrically attracted and stick to one another.
The unit of electric charge, the coulomb, is the charge on a A. quark. B. specific number of neutrons. C. single electron. D. specific large number of electrons. E. neutron.
D. specific large number of electrons.
Touch a 5000-V charged balloon and you're not harmed because, although the energy/charge ratio is high, there is A. no way this large amount of energy can transfer under normal conditions. B. enough resistance between you and the balloon to be safe. C. very little conduction of electricity. D. very little energy on the balloon. E. ...Wait a minute? Don't ever touch a 5000-V balloon?
D. very little energy on the balloon.
The number of electrons that move about the nucleus of an electrically neutral atom is the same as the number of A. protons + neutrons in the nucleus. B. quarks in the nucleus. C. neutrons in the nucleus. D. None of these. E. protons in the nucleus.
E. protons in the nucleus.
Distinguish between electric potential energy and electric potential. Which is a vector quantity and which is a scalar quantity?
Electric potential energy (PE) is the energy measured in joules that a charged object possesses by virtue of its location in an electric field. Electric potential is that PE per unit of charge (PE/q) measured in volts (). Both are scalar quantities.
Why is charge usually transferred by electrons rather than by protons?
Electrons are loosely bound on the outside of atoms, whereas protons are very tightly bound within the atomic nuclei.
Why are materials such as glass and rubber good insulators?
Electrons are tightly bound to their atoms, making them poor conductors of heat
What happens to electrons in any charging process? Electrons transfer from one place to another. Electrons are created. Electrons are destroyed. Electrons stay in place as protons are transferred from one place to another.
Electrons transfer from one place to another.
electric potential energy
Energy a charge has due to its location in an electric field
A pair of charged particles repel each other with a force F. If the charge of one particle is doubled and the distance between them is doubled, the force will be F. F/2. F/4. 2 F.
F/2. Coulomb's Law tells us that the force between two charges is directly proportional to the size of the charge and inversely proportional to the square of the distances. Reading the symbols, if the size of the charge becomes 2Q, the force increases to 2F, and if the distance increases to 2R, then the force decreases to ¼F. Twice divided by four gives half the initial force, F/2.
What kind of charging occurs during thunderstorms?
Ice crystals are charged by friction and the ground is charged by induction.
What is an electric dipole?
In an electric dipole, positive and negative charges are separated on opposite sides of an object.
If a proton at a particular distance from a charged particle is repelled with a given force, by how much will the force decrease when the proton is three times farther away from the particle? When it is five times farther away?
It decreases to 1/9 its original value; to 1/25 its original value
What does it mean when we say that charge is b) conserved
It means that charge can be neither created nor destroyed but can be transferred from one object to another. The net charge is conserved.
What does it mean when we say that charge is: a) quantized
It means that charge comes in discrete packages - multiples of the charge on an electron
In a humorous vein, if you rub a balloon on your hair and put your head to the wall, will it stick to the wall like the balloon would?
It would, if you were an airhead—that is, if the mass of your head were about that of the balloon, so that the force produced would be evident.
Beneath the complexities of electrical phenomena, there lies a fundamental rule from which nearly all other effects stem. What is this fundamental rule?
Like charges repel; opposite charges attract.
conductor
Materials in which one or more of the electrons in the outer shell of its atoms are not anchored to the nuclei of particular atoms but are free to wander in the material - Example: Metals such as copper and aluminum
What is meant by conservation of charge? The amount of charge in every nucleus is the same. All electrons have the same electric charge. Whenever an electron is created, an equal and oppositely charged proton is also created. Net charge cannot be created or destroyed.
Net charge cannot be created or destroyed.
Are semiconductors similar to superconductors?
No, quite different. The defining property of a semiconductor is that it can be made to behave as a conductor or an insulator. The defining property of a superconductor is that it has zero resistance to the flow of charge. Semiconductors and superconductors have almost nothing in common.
A balloon may easily be charged to several thousand volts. Does that mean it has several thousand joules of energy? Explain.
No. Energy is voltage times charge, so you need a coulomb of charge to get several thousand joules of energy.
Why are metals good conductors of both heat and electricity?
The outer shell electrons in metals are free to move from atom to atom.
A negatively charged rod is brought close to some small pieces of neutral paper. The positive sides of the molecules in the paper are attracted to the rod and the negative sides of the molecules are repelled. Why don't these attractive and repulsive forces cancel out?
The positive sides are simply closer to the rod. They therefore experience a greater electrical force than the farther away negative sides. hence we say that closeness wins. Can you see that a positive rod would still produce attraction?
The proton that is the nucleus of the hydrogen atom attracts the electron that orbits it. Relative to this force, does the electron attract the proton with less force, with more force, or with the same amount of force?
The same amount of force, in accord with Newton's third law—basic mechanics! Recall that a force is an interaction between two things—in this case, between the proton and the electron. They pull on each other equally.
How do you compare the charge of the electron versus the charge of the proton?
The same magnitude, but opposite signs.
At some automobile toll booths, a thin metal wire protrudes from the road, making contact with cars before they reach the toll collector. What is the purpose of this wire?
The wires at toll-collecting stations are used to discharge the cars so that paying the toll is not a shocking experience for the driver or the collector.
How does the concept of force for electrical phenomena compare with the mechanical forces described in Newton's laws of motion?
There's no difference! The concept of force is general, whether pushes or pulls are created by muscular effort, gravity, or electricity—all are measured in the same units: newtons.
Two isolated charges repel each other when approached. What can we say about these charges? One has no charge. They have different types of charge. One has more charge than the other. They have the same type of charge
They have the same type of charge.
We have learned that the gravitational fields of the Sun and Earth extend to infinity. Can we say the same about the electric fields that surround electrons and protons?
Yes, gravitational and electric fields are both auras of energy, one depending on mass and the other on charge, both with strengths that diminish via the inverse-square law.
Are the lines of force shown in the three configurations in Figure 22.19 also electric field lines?
Yes, these imaginary lines, whether we call them lines of force or electric field lines, indicate the direction of the electric field.
If you scuff electrons onto your feet while you walk across a rug, are you negatively or positively charged?
You have more electrons after you scuff your feet, so you are negatively charged (and the rug is positively charged).
What is the net charge of a charged capacitor?
Zero, because the charges on its two plates are equal in number and opposite in sign. Even when the capacitor is discharged—say, by providing a path for charge flow between the oppositely charged plates—the net charge of the capacitor remains zero because each plate then has zero charge.
Yes, these imaginary lines, whether we call them lines of force or electric field lines, indicate the direction of the electric field.
Zero, in all cases.
electric field
a field of force surrounding a charged particle
electric dipoles
a little more negative charge on one side of the molecule than on the other
An electric field is ___________. the same as a gravitational field a vector quantity a source of voltage an invisible force
a vector quantity
Which molecule is an example of a common electric dipole? A nitrogen molecule An oxygen molecule A carbon dioxide molecule A water molecule
a water molecule
A positively charged balloon touching a wooden wall polarizes molecules in the wall. All of the above pushes positive charge in the wall away from it. pulls negative charge on the wall surface toward it.
all of the above. This is straightforward charge polarization. The positively-charged balloon pulls negative charge towards the wall and pushes positives away. The result is net attraction between the wall and the balloon.
electrically polarized
an atom or molecule in which the charges are aligned so that one side is slightly more positive or negative than the opposite side
Two charged particles held close to each other are released. As they move, their speeds increase. Therefore, their charges have Need more information the same sign. opposite signs. Either of these
either of these. Whoa! Whatever the signs of charge, when released they will accelerate due to the force each experience. If the charges are of like sign, they will accelerate away from each other with increasing speeds. If the charges are of opposite signs, they will accelerate toward each other with increasing speeds. Speeds would increase in either case
electric potential equals
electric potential energy/ charge
Van de Graaff generator
electrical device that produces a high voltage by building up a charge of static electricity
A party balloon of high voltage likely has low electrical resistance. charge. energy. All of the above
energy. It is important to view voltage as a ratio of energy per charge. Rub a balloon on your hair and it may be at 1000 volts. But the amount of charge it acquires is likely about a millionth of a coulomb. From V = E/q, we see E = Vq, which is (1000 V)(0.000,001 C) = 0.001 J—a very low amount of energy.
coulomb's law
for 2 charged objects that are much smaller than the distance between them, the force between the 2 objects varies directly as the product of their charges and inversely as the square of the separation distance
Fundamental to conductors are Both of these in various proportions free electrons. bound electrons. None of the above
free electrons. Many conductors are metallic materials due to their atomic bonding. Fundamental to conductors is the freeness of electrons that can move among atoms within the conducting material.
As in the video, we apply a charge + Q to the half-shell that carries the electroscope. This time, we also apply a charge - Q to the other half-shell. When we bring the two halves together, we observe that the electroscope discharges, just as in the video. What does the electroscope needle do when you separate the two half-shells again? It does not deflect at all. It deflects more than it did at the end of the video. It deflects the same amount as at end of the video. It deflects less than it did at the end of the video
it does not deflect at all
semiconductors
material that can be made to behave sometimes as an insulator and sometimes as a conductor.
When we say that electric charge is conserved, we mean that no example has ever been found where None of the above net charge has been created or destroyed. the net charge on an object has changed. the net amount of charge on an object has increased.
net charge has been created or destroyed.
Coulomb's law is most similar to which of these laws or definitions? Electric potential The conservation of energy Archimedes' laws of hydrostatics Newton's law of gravity
newton's law of gravity
The electric field around an isolated electron has a certain strength 1 cm from the electron. The electric field strength 2 cm from the electron is None of the above twice as much. half as much. the same.
none of the above. The electric field about an isolated electron takes the shape of straight lines the strength of which diminishes with distance in accord with the inverse-square law. So twice the distance from the electron means one-fourth the electric field strength. Not listed, so the choice is (d).
What is the sign of the charge of the particle in this case?
positive
When stripping electrons from an atom, the atom becomes a an isotope. different element. negative ion. positive ion.
positive ion. An atom has neutral charge because there are an equal number of positive protons and negative electrons. In contrast, an ion has an unequal number of protons and electrons. When electrons are stripped from an atom more protons than electrons means the atom has a positive charge and becomes a positive ion.
electrical force
positives and negatives. like kinds repel and unlike kinds attract
induction
putting a charged object near a place without physical contact . happens during thunderstorms
Consider the situation in the figure below, where two charged rods are placed a distance dd on either side of an aluminum can. What does the can do?
stays still
electric shielding
the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials
conservation of change
the principle that net electric charge is neither created or destroyed but it is transferrable from one object to another.
Electrons in a metal paper clip don't fly off the surface because they are strongly bonded to the metal surface. they are attracted to an equal number of protons. mutual repulsion is incomplete. All of the above
they are attracted to an equal number of protons. The electrons are electrically attracted to an equal number of protons in an atom, which prevents them from flying off surfaces. This mutual attraction, rather than mutual repulsion keeps them on the paper clip.
Electric potential, unlike electric potential energy, is measured in units of _________. conduction coulombs volts joules
volts
Most atoms normally have a net charge that is positive in the nucleus and slightly more negative in its electrons negative positive zero
zero
The electric field inside the dome of a highly charged Van de Graaff generator is _________. the inverse of the field close to its outer surface at a potential that depends on the amount of surface charge zero a source of energy
zero
The net charge on a polarized molecule is normally _________. zero re-oriented opposite to the charge that produces the polarization the same as the charge that produces the polarization
zero
How does one coulomb of charge compare with the charge of a single electron?
A coulomb of charge is the charge associated with 6.25 × 1018 electrons.
When you remove your wool suit from the dry cleaner's garment bag, the bag becomes positively charged. Explain how this occurs.
When the wool and plastic rub against each other, electrons are rubbed from the plastic onto the wool. The deficiency of electrons on the plastic bag results in its positive charge.
conserved charge
charge can be neither created or destroyed but can be transferred from one object to another.
quantized charge
charge comes in discrete packages- multiples of the charge on an electron
A highly charged party balloon is not dangerous when it _________. has an insulating rather than a conducting surface is electrically grounded contains equal numbers of positive and negative charges contains little overall energy
contains little overall energy
A thin stream of water bends toward a negatively charged rod. When a positively charged rod is placed near the stream, it will bend in the
same direction
contact
substances rubbed together or lightly touched
How does the flow of current differ in a superconductor compared with the flow in ordinary conductors?
Superconductors have infinite conductivity (current flows forever), whereas ordinary conductors have a small resistance to the flow of electric charge.
How does the charge of an electron differ from the charge of a proton?
The charge of an electron is equal in magnitude, but opposite in sign, to the charge of a proton.
Each coulomb of charge that flows across a 12-volt potential difference has 12 watts. 12 amperes of current. 12 newtons of force. 12 joules of energy.
12 joules of energy.Voltage is defined in terms of the amount of energy (joules) per charge. A 12-volt potential difference imparts 12 joules of energy to each coulomb of charge.
Which of the figures best represents the charge distribution on the inner and outer walls of the conductor?
3
superconductors
A material that acquires zero resistance (infinite conductivity) to the flow of charge. Once electric current is established in a superconductor, the electrons flow indefinitely. With no electrical resistance, current passes through a superconductor without losing energy; no heat loss occurs when charges flow.
What is a positive ion? What is a negative ion?
A positive ion is a neutral atom that has lost one or more electrons. A negative ion is a neutral atom that has gained one or more electrons.
What kind of charging occurs when you slide your body across a plastic surface?
Charging by friction occurs. Electrons are transferred when one object rubs against another.
To say that electric charge is conserved is to say that electric charge A. may occur in an infinite variety of quantities. B. is a whole number multiple of the charge of one electron. C. will interact with neighboring electric charges. D. can be neither created nor destroyed. E. is sometimes negative.
D. can be neither created nor destroyed.
Cite a major difference between electrical and gravitational forces?
Electrical forces can attract or repel, whereas gravitational forces only attract.
insulators
Materials in which electrons are tightly bound and belong to particular atoms and are not free to wander about among other atoms in the material, making them flow - Example: Rubber, glass
How much energy is given to each coulomb of charge that flows through a 6- V battery? 6 joules 6 watts 0.167 watts 0.167 joules
6 joules
What is the unit of charge?
1 coulomb, the standard unit of charge, is the electric charge of 6.25 billion billion electrons.
Two conducting spheres are each given a charge QQ. The radius of the larger sphere is three times greater than that of the smaller sphere. If the electric field just outside of the smaller sphere is E0E0, then the electric field just outside of the larger sphere is
1/9 E0
When charges mutually repel and distribute themselves on the surface of conductors, what becomes of the electric field inside the conductor? The charges arrange themselves to make the field inside the conductor the same nonzero value everywhere. The charges arrange themselves to make the field zero only at the center of mass of the conductor. The charges arrange themselves to make the field inside the conductor radially symmetric and inverse square in strength. The charges arrange themselves to make the field inside the conductor zero.
The charges arrange themselves to make the field inside the conductor zero.
How is the direction of an electric field defined? The direction of the field is the direction of the force on an electron. A field is not a vector, so it does not have a direction. The direction of the field is the direction of the force on a neutron. The direction of the field is the direction of the force on a positive test charge.
The direction of the field is the direction of the force on a positive test charge.
Where is the energy stored in a capacitor?
The energy is stored in the electric field between the plates.
What happens to the force between two charges if they are moved to three times the distance?
The force decreases nine times
A glass marble is rubbed against a piece of silk. As a result the piece of fabric acquires extra electrons. What happens to the glass marble?
The marble acquires a positive charge and attracts the piece of silk The marble has lost the same number of electrons acquired by the piece of silk
Electrons are transferred from the fur to the rod. The rod is then negatively charged. Is the fur charged? How much compared to the rod?
The net charge at the beginning was zero. I transferred electrons to the rod, that means the fur has less electrons, and it will be positively charged. Remember the net charge has to be conserved, so the fur will have equal but opposite charge to the rod