30 terms

# CH 22

#### Terms in this set (...)

What term is used for electricity at rest?
Electrostatics is a branch of electricity that is associated with the charges that are at rest. Here electro refers to electricity and static refers to rest. It deals with the electric field due to static charges and force between static charges and their behavior with in the vicinity of electric field.
Why does the gravitational force between earth and moon predominate over electrical forces?
This is because both Earth and the Moon contain an equal numbers of positive and negative charges. Thus, there is hardly any repulsion or attraction by electrical charges. Because of the very large masses of Earth and the Moon, gravitational forces predominate over electrical forces.
What part of an atom is positively charges and what part is negatively charged?
The nucleus of the atom is positively charged, while the outer shell of the atom is negatively charged.
How does the charge of one electron compare to that of another electron? How does it compare with the charge of a proton?
Electrons have the same kinds of charges, whereas the charge of an electron is opposite to that of a proton. However, the magnitudes of charges on an electron and on a proton are the same.
What is normally the net charge of an atom?
Zero
What is a positive ion? A negative ion?
A positive ion is created when electrons in the outer most of a neutral atom are removed. A negative ion is created when extra electrons are added to the neutral atom.
What is meant by saying charge is conserved?
It means that when we charge something, no electrons are created or destroyed; they are simply transferred from one material to another.
What is meant by saying charge is quantized?
Since electrons cannot be divided further, the charge of the object is a whole number multiple of the charge if an electron. Thus, we say the charge is quantized.
What particle has exactly one quantum unit of charge?
Either an electron or a proton.
How does one coulomb of charge compare with the charge of a single electron?
1 coulomb charge is equal to the charge associated with 6.25x〖10〗^18 electrons.
How is Coulomb's law similar to Newton's lar of gravitation? How is it different?
Coulomb's law is similar to Newton's law in that force is proportional to the product of the amount of charges and inversely proportional to the square of the distance between them. And, similar to G we have R. The difference is that the value of K is much larger than the value of G, making the Coulomb force a very strong force.
Why are metals good conductors both of heat and of electricity?
Metal contains free electrons that can move from one end to another. Thus metals are good conductors of electricity and heat.
Why are materials such as glass and rubber good insulators?
Electrons in rubber and glass are tightly bound to their atoms. They are not free to move among other atoms in materials. Because of this it is not possible for them to carry either electricity or heat from one end to another, and thus they are insulators.
How does semiconductor differ from a conductor or an insulator?
The resistance of a semiconductor lies between that of a metal and that of an insulator. However, a semiconductor can sometimes be made to behave as an insulator and sometimes as a conductor.
What is a transistor composed of, and what are some of its functions?
Transistors are composed of a layer of semiconductor materials. They can be used to control the flow of currents in circuits, to detect and amplify radio signals, to produce oscillators in transmitters, and to act as digital switches in electronic circuits.
How does the flow of current differ in a superconductor compared with the flow in ordinary conductors?
An ordinary conductor has only a small resistance to the flow of electric charge. However, in super conductors the electric current passes with zero resistance.
What happens to electrons in any charging process?
They are simply transferred from one material to another.
Cite an example of something charges by friction.
The charge induced in a comb while combing hair is an example of charging by friction.
Cite an example of something charged by contact.
Two things can be charged either by physical contact, that is when they are rubbed together, or through conduction. An example is a glass rod is rubbed with silk, then there is a transfer of electrons from the glass to the silk. Loss of electrons from the rod gives it a positive charge and due to the gain of electrons, silk is left with a negative charge. Thus the two objects glass rod and silk, get charged due to mutual contact.
Give an example of something charged by induction.
An example of induction using negatively charged object and an initially uncharged conductor. Bring the negatively charged object close, but not touching the conductor. Electrons on the conductor will be repelled from the area nearest the charged object. Connect the conductor to the ground. The electrons on the conductor want to get as far away from the negatively charged object, so some of them flow to the ground. Remove the ground connection. This leaves the conductor with a deficit of electrons. Removed the charged object. The conductor is now positively charged.
What is the primary purpose of a lightning rod?
Lightening rod provides less resistance path for the large amount of electric current that is produced during the lightening and prevents the damage caused by lightening. If sufficient charge does not leak from the air to the rod and lightning strikes anyway, it may be attracted to the rod and take a direct path to the ground.
How does an electrically polarized object differ from an electrically charged object?
The positive and negative charges of an electrically polarized object are separated. An electrically charged object has a net positive charge or net negative charge.
What is an electric diploe?
Magnitude if electric field due to a point charge is given by E= 1/(4πε_0 ) q/r^2 When two equal and opposite charges are separated by a distance, they constitute an electric dipole.
How is the magnitude of an electric field defined? Its direction?
The magnitude of the electric field at any point is defined as the force per unit charge. The electric force F acting on an object of a charge q is E= F/q. Here E is the magnitude of the electric field. The direction of electric field is the same in the direction of electric force.
Why is there no electric field at the center of a charged spherical conductor?
At the center of a charged spherical conductor, mutual cancellation of forces occurs, resulting in zero net force at the center. So the electric field is zero.
When charges mutually repel and distribute themselves on the surface of conductors, what becomes of the electric field inside the conductor?
There is no charge left inside the conductor and no electric field inside the conductor.
How much energy is given to each coulomb of charge that flows through a 1.5 V battery?
U= qV U= potential energy, q= charge on the particle and V= potential difference.
U= (1C)(1.5 V)
= 1.5 J.
Hence energy given to 1 C is 1.5 J.
A balloon may easily be charged to several thousand volts. Does this mean it has several thousand joules of energy? Explain.
No, it cannot have thousand joules of energy. This is because the charge given to the balloon is very small. Thus the product of the charge and volts become smaller in quantity.
Where is the energy stored in a capacitor?
The energy is stored in the electric field between the plates of the capacitor.
What is the magnitude of the electric field inside the dome of a charged can de Graaff generator?
Zero.