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What is matter, and in what three states is it found?
- Anything that occupies space and has weight.
- Solids
- Liquids
- Gases.
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What is an element?
A substance which cannot be reduced to a simpler substance by chemical means.
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What is a compound?
A substance consisting of two or more elements.
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What is the difference between a compound and a mixture?
- A compound is a chemical combination of elements that cannot be separated by physical means.
- A mixture is a physical combination of elements and compounds that are not chemically combined.
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What is a molecule?
A chemical combination of two or more atoms.
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What are the three types of subatomic particles, and what are their charges?
Electrons-negative, protons-positive, and neutrons-neutral.
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What is energy of motion called?
Kinetic energy.
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How is invisible light changed to visible light in a fluorescent light?
Invisible light photons (ultraviolet) bombard the phosphor atom in the light tube. The phosphor atoms emit visible light photons.
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What determines the valence of an atom?
The number of electrons in the outer shell.
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What is an ion?
An atom with more or less than its normal number of electrons.
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What determines whether a substance is a conductor or an insulator?
The number of valence electrons.
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How is a negative charge created in a neutral body?
Through the accumulation of excess electrons.
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How are static charges created?
By friction.
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What is the electrical charge of an atom which contains 8 protons and 11 electrons?
Negative.
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What is the relationship between charged bodies?
Like charges repel, and unlike charges attract with a force directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
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What is an electrostatic field?
The space between and around charged bodies.
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In what direction are electrostatic lines of force drawn?
Leaving positive, entering negative.
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What are some examples of electrical equipment which use magnetism?
Motors, generators, speakers, computers, televisions, tape recorders, and many others.
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What are magnetic materials?
Those materials that are attracted by magnets and have the ability to become magnetized.
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What characteristics do all ferromagnetic materials have in common?
The relative ease with which they are magnetized.
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What type of magnetic material should be used to make a temporary magnet?
A material that exhibits low reluctance and high permeability, such as iron or soft steel.
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What is retentivity?
The ability of a material to retain magnetism.
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How does the law of magnetic poles relate to the law of electric charges?
They are very similar; like charges repel, unlike charges attract, like poles repel�unlike poles attract.
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A compass is located at the geographical North Pole. In which direction would its needle point?
To the magnetic north pole.
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Using Weber,s molecular theory of magnetism, describe the polarity of the magnetic poles produced by stroking a magnetic material from right to left with the south pole of a magnet.
South pole at the right, north pole at the left.
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What is the difference between the domain theory and Weber's theory of magnetism?
The domain theory is based upon the electron spin principle; Weber,s theory uses the concept of tiny molecular magnets.
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What is a magnetic line of force?
An imaginary line used to illustrate magnetic effects.
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In what way do magnetic lines of force differ from electrostatic lines of force?
Electrostatic lines of force do not form closed loops.
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How should a delicate instrument be protected from a magnetic field?
By shielding or surrounding the instrument with a soft iron case, called a magnetic shield or screen.
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How should bar magnets be stored?
In pairs, with opposite poles together to provide a complete path for magnetic flux.
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What is the definition of energy?
The ability to do work.
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What type of energy does a rolling stone have?
Kinetic energy.
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What kind of energy does the stone have if it is at rest at the top of a hill?
Potential energy.
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What term describes voltage or emf?
Difference of potential.
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Convert 2.1 kV to volts.
2100 volts.
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Express the following in more simple terms. (a) 250,000 volts, (b) 25,000,000 microvolts, (c) 0.001 millivolt.
(a) 250 kV, (b) 25 V, (c) 1 �V.
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A device which supplies a voltage is commonly referred to by what name?
A voltage source.
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Name the six methods of producing a voltage.
Friction, pressure, heat, light, chemical action, and magnetism.
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The piezoelectric effect is an example of a voltage being produced by what method?
Pressure.
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A thermocouple is a device that produces voltage by what method?
Heat.
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A battery uses what method to produce a voltage?
Chemical.
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A generator uses what method to produce a voltage?
Magnetic.
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According to electron theory, an electric current flows from what potential to what potential?
Electron theory assumes that electron flow is from negative to positive.
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The effects of directed drift take place at what rate of speed?
The speed of light (186,000 miles per second, 300,000,000 meters per second).
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What is the relationship of current to voltage in a circuit?
Current increases as voltage increases.
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Convert 350 mA to amperes.
0.35 amperes.
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When would silver be used as a conductor in preference to copper?
When the need for conductivity is great enough to justify the additional expense.
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Which wire has the least resistance? Wire A-copper, 1000 circular mils, 6 inches long. Wire B-copper, 2000 circular mils, 11 inches long.
Wire B.
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Which temperature coefficient indicates a material whose resistance increases as temperature increases?
Positive.
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What term describes a material whose resistance remains relatively constant with changes in temperature?
Zero temperature coefficient.
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What is the unit of conductance and what other term is sometimes used?
The mho (v), siemens.
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What is the relationship between conductance and resistance?
They are reciprocals of each other.
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What does the wattage rating of a resistor indicate?
Its ability to dissipate heat.
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What are the two disadvantages of carbon-type resistors?
- Change value with age.
- Limited power capacity.
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What type resistor should be used to overcome the disadvantages of the carbon resistor?
The wirewound resistor.
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Describe the differences between the rheostat connections and those of the potentiometer.
The rheostat may have two connections, one fixed and one moveable; the potentiometer always has three connections, one moveable and two fixed.
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Which type of variable resistor should you select for controlling a large amount of current?
The rheostat.
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A carbon resistor has a resistance of 50 ohms, and a tolerance of 5 percent. What are the colors of bands one, two, three, and four, respectively?
The bands are green, black, black, and gold.
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A carbon resistor has the following color bands: The first band is yellow, followed by violet, yellow, and silver. What is the ohmic value of the resistor?
470,000 ohms (470 kilohms).
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The same resistor mentioned in question 63 has a yellow fifth band. What does this signify?
The resistor,s chance of failure is 0.001 percent for 1000 hours of operation.
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A resistor is handed to you for identification with the following color code: the first band is blue, followed by gray, green, gold, and brown. What is the resistor's value?
6,800,000 ohms (6.8 megohms), with 5% tolerance, and a 1% reliability level.
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