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What term is used for "electricity at rest"? |
Electrostatics |
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Why does the gravitational force between Earth and Moon predominate over electrical forces? |
The electric force between Earth and Moon cancels out because they have an equal number of positive and negative charges. |
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Which part of an atom is positively charged, and which part is negatively charged? |
The nucleus is positively charged and the electron cloud is negatively charged. |
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How does the charge of one electron compare to that of another electron? How does it compare with the charge of a proton? How do the masses of protons and electrons compare? |
All electrons have the same charge. Electron charge is equal and opposite to the proton charge. A proton has 1800 times the mass of an electron. |
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What is the most common net charge of an atom? |
Neutral |
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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. |
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What is meant by conservation of charge? |
Net charge cannot be created or destroyed. |
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What is meant by saying that charge is quantized? |
All charged objects have a charge that is an integer multiple of the charge of an electron. |
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Which particle has exactly one quantum unit of charge? |
Proton |
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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 × 10 18 electrons. |
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How is Coulomb’s law similar to Newton’s law of gravitation? How is it different? |
Newton’s law of gravitation is attractive, whereas Coulomb’s law is attractive or repulsive. Both are proportional to the inverse square of distance. |
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Why are metals good conductors of both heat and electricity? |
The outer shell electrons in metals are free to move from atom to atom. |
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Why are materials such as glass and rubber good insulators? |
Electrons are tightly bound to their atoms, making them poor conductors of heat. |
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How does a semiconductor differ from a conductor or an insulator? |
A semiconductor is neither a good conductor nor a good insulator – it has a middle range of resistivity. |
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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. |
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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. |
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What happens to electrons in any charging process? |
Electrons transfer from one place to another. |
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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. |
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What kind of charging occurs during thunderstorms? |
Ice crystals are charged by friction and the ground is charged by induction. |
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What is the primary purpose of a lightning rod? |
To prevent a fire caused by lightning. |
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In terms of net charge, how does an electrically polarized object differ from an electrically charged object? |
An electrically polarized object can have zero net charge, while a charged object cannot have zero net charge. |
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What is an electric dipole? |
In an electric dipole, positive and negative charges are separated on opposite sides of an object. |
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Which molecule is an example of a common electric dipole? |
A water molecule |
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Give two examples of common force fields and name the sources of these fields. |
Gravity fields made by mass, electric fields made by charge |
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How is the direction of an electric field defined? |
The direction of the field is the direction of the force on a positive test charge. |
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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. |
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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 zero. |
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How much energy is given to each coulomb of charge that flows through a 1.5-V battery? |
1.5 joules |
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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. |
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Where is the energy stored in a capacitor? |
The energy is stored in the electric field between the plates. |
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