Why does the gravitational force between Earth and Moon predominate over electrical forces?
answer
The electric force between Earth and Moon cancels out because they have an equal number of positive and negative charges.
question
Which part of an atom is positively charged, and which part is negatively charged?
answer
The nucleus is positively charged and the electron cloud is negatively charged.
question
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?
answer
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.
question
What is the most common net charge of an atom?
answer
Neutral
question
What is a positive ion? What is a negative ion?
answer
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.
question
What is meant by conservation of charge?
answer
Net charge cannot be created or destroyed.
question
What is meant by saying that charge is quantized?
answer
All charged objects have a charge that is an integer multiple of the charge of an electron.
question
Which particle has exactly one quantum unit of charge?
answer
Proton
question
How does one coulomb of charge compare with the charge of a single electron?
answer
A coulomb of charge is the charge associated with 6.25 × 10 18 electrons.
question
How is Coulomb's law similar to Newton's law of gravitation? How is it different?
answer
Newton's law of gravitation is attractive, whereas Coulomb's law is attractive or repulsive. Both are proportional to the inverse square of distance.
question
Why are metals good conductors of both heat and electricity?
answer
The outer shell electrons in metals are free to move from atom to atom.
question
Why are materials such as glass and rubber good insulators?
answer
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?
answer
A semiconductor is neither a good conductor nor a good insulator - it has a middle range of resistivity.
question
What is a transistor composed of, and what are some of its functions?
answer
A transistor is made of thin layers of semiconducting materials sandwiched together. It can be a switch, an oscillator, or an amplifier.
question
How does the flow of current differ in a superconductor compared with the flow in ordinary conductors?
answer
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?
answer
Electrons transfer from one place to another.
question
What kind of charging occurs when you slide your body across a plastic surface?
answer
Charging by friction occurs. Electrons are transferred when one object rubs against another.
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What kind of charging occurs during thunderstorms?
answer
Ice crystals are charged by friction and the ground is charged by induction.
question
What is the primary purpose of a lightning rod?
answer
To prevent a fire caused by lightning.
question
In terms of net charge, how does an electrically polarized object differ from an electrically charged object?
answer
An electrically polarized object can have zero net charge, while a charged object cannot have zero net charge.
question
What is an electric dipole?
answer
In an electric dipole, positive and negative charges are separated on opposite sides of an object.
question
Which molecule is an example of a common electric dipole?
answer
A water molecule
question
Give two examples of common force fields and name the sources of these fields.
answer
Gravity fields made by mass, electric fields made by charge
question
How is the direction of an electric field defined?
answer
The direction of the field is the direction of the force on a positive test charge.
question
Why is there no electric field at the center of a charged spherical metal ball?
answer
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.
question
When charges mutually repel and distribute themselves on the surface of conductors, what becomes of the electric field inside the conductor?
answer
The charges arrange themselves to make the field inside the conductor zero.
question
How much energy is given to each coulomb of charge that flows through a 1.5-V battery?
answer
1.5 joules
question
A balloon may easily be charged to several thousand volts. Does that mean it has several thousand joules of energy? Explain.
answer
No. Energy is voltage times charge, so you need a coulomb of charge to get several thousand joules of energy.
question
Where is the energy stored in a capacitor?
answer
The energy is stored in the electric field between the plates.
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