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83 Cards in this Set
- Front
- Back
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What constitutes a capacitor? |
Two conductors separated by an insulator |
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What is the purpose of a capacitor? |
It stores electrical energy in electrostatic fields. |
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Does a capacitor in an AC circuit cause the current to lead or lag the voltage? |
It causes the current to lead the voltage |
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What is the basic unit of the capacitance? |
The Farad. |
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Why should electrolytic capacitors not be used in an AC current? |
They are polarized. |
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What is meant by inductance? |
The ability to store electrical energy in electromagnetic fields. |
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What is an example of an inductor used in a magneto? |
The coil. |
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Does an inductor in an AC circuit cause the current to lead or lag the voltage? |
It causes the current to lad behind the voltage. |
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What is the basic unit of inductance? |
The Henry. |
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How can you find the polarity of an electromagnet? |
Hold the electromagnet in your left hand with your fingers encircling the coil in the direction electrons flow (negative to positive). Your thumb will point to the North Pole of the electromagnet. |
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What is meant by impedance? |
The total opposition to the flow of alternating current. |
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In what units is impedance measured? |
The Ohms. |
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What are the five sources of electrical energy? |
Magnetism, chemical energy, light, heat, and pressure. |
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What is the basic unit of power in a DC circuit? |
The Watt. |
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What is meant by kilowatt? |
1,000 watts. |
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What is meant by megawatt? |
1,000,000 watts. |
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What is the formula for power in a DC circuit? |
Power = voltage times current (P = E x I) |
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What is the relationship between mechanical and electrical power? |
1 horsepower = 746 watts |
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What is meant by true power in an AC circuit? |
The product of the circuit voltage and the current that is in phase with the voltage. |
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In what units it true power expressed? |
In Watts. |
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What is meant by apparent power in an AC circuit? |
The product of the circuit voltage and the circuit current. |
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In what units is apparent power expressed? |
In volt-amps. |
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What is meant by reactive power in an AC circuit? |
The power consumed in the inductive and capacitive reactances in an AC circuit. |
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In what units is reactive power expressed? |
In volt-amps reactive (VAR) or kilovolt-amps reactive (KVAR). |
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What is meant by power factor in an AC circuit? |
The ratio of true power to apparent power. It is also the ratio of the circuit resistance to circuit impedance. |
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Which law of electricity is the most important for an aircraft mechanic to know? |
Ohms law. |
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What are the elements of Ohm’s law? |
Voltage = E, current = I, and resistance = R ( volts, amps, and ohms) |
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What is voltage? |
Electrical Pressure. |
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What is the basic unit of voltage? |
The volt. |
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What instrument is used to measure voltage? |
A Voltmeter. |
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To measure voltage, is a voltmeter placed in series or in parallel with the source of voltage? |
In parallel. |
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What is electrical current? |
The flow of electrons in a circuit. |
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What is the basic unit of current flow? |
The ampere (amps). |
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What part of the amp is a milliamp? |
One thousandth (0.001) of an amp. |
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What instrument is used to measure current flow? |
An ammeter. |
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What two things happen when the current flows through a conductor? |
Heat is generated and a magnetic field surrounds the conductor. |
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To measure current through a component, is an ammeter placed in parallel or in series with the component? |
In series. |
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What is meant by resistance in an electrical circuit? |
The opposition of the flow of electrons. |
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What is the basic unit of electrical resistance? |
The Ohm. |
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What is a megohm? |
One million (1,000,000) ohms. |
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What four things affect the resistance of an electrical conductor? |
The material, the cross sectional area, the length, and the temperature. |
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What instrument is used to measure electrical resistance? |
An Ohmmeter. |
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How can you tell the resistance of a composition resistor? |
By a series of colored bands around one end of the resistor. |
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What is meant by continuity in an electrical circuit? |
The circuit is continuous (or complete) when the electrons can flow from one terminal of the power source to the other. |
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What instrument is used to measure continuity in an electrical circuit? |
An ohmmeter. |
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When measuring resistance of a component with an ohmmeter, should the circuit be energized? |
No, there should be no power on the circuit. |
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What three things must an electric circuit contain? |
A source of electrical energy, a load to use the energy, and conductors to join the source and the load. |
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What are three types of DC circuits with regard to the placement of the various circuit components? |
Series, parallel, and series-parallel |
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What is the name of the law that describes the relationship in an electrical circuit of the voltage, current and resistance? |
Ohm’s law. |
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What is the basic equation of ohms law? |
E = I x R ( voltage equals current times resistance) |
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What formula is used to find current when voltage and resistance are known? |
I = E/R (current equals voltage divided by resistance). |
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What formula is used to find resistance wham voltage and current are known? |
R = E/I (resistance equals voltage divided by current). |
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What happens to the current in a conductor if the length of the conductor is doubled with all the other parameters unchanged? |
It would decrease to one half. |
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What is the voltage across each resistor connected in parallel across a 12-volt battery? |
12 volts. |
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How much current flows through each of three resistors connected in series if the total current is 3 amps? |
3 amps. |
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What is the total resistance of three 12-ohm resistors connected in series? |
36 ohms. |
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What is the total resistance of three 12-ohm resistors connected in parallel? |
4 ohms. |
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What is meant by the capacity rating of a lead-acid battery? |
The number of hours a battery can supply a given current flow. |
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In what units is battery capacity expressed? |
In ampere-hours. |
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What electrolyte is used in a lead-acid battery? |
A mixture of sulfuric acid and water. |
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Does the specific gravity of the electrolyte in a lead-acid battery increased or decrease as the battery becomes discharged? |
It decreases. |
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What is the specific gravity of a fully charged lead-acid battery? |
Between 1.275 and 1.300. |
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How many cells are there in a 24-volt lead-acid battery? |
12 |
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What is the range of the temperatures of the electrolyte in a lead-acid battery that does not require a correction when measuring its specific gravity? |
Between 70 degrees F and 90 degrees F. |
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What instrument is used to measure the specific gravity of the electrolyte in a lead-acid battery? |
A hydrometer. |
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How do you treat a lead-acid battery compartment to protect it from corrosion? |
Paint it with an asphaltic (tar-base) paint or with a polyurethane enamel. |
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How do you treat a lead-acid battery compartment to protect it from corrosion? |
Paint it with an asphaltic (tar-base) paint or with a polyurethane enamel. |
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What is used to neutralize spilled electrolyte from a lead-acid battery? |
A solution of bicarbonate of soda and water. |
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How do you treat a lead-acid battery compartment to protect it from corrosion? |
Paint it with an asphaltic (tar-base) paint or with a polyurethane enamel. |
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What is used to neutralize spilled electrolyte from a lead-acid battery? |
A solution of bicarbonate of soda and water. |
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How high should the electrolyte level be in a properly serviced lead-acid battery? |
Only up to the level of the indicator in the cell. |
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Why is the closed-circuit voltage of a lead-acid battery lower than its open-circuit voltage? |
Voltage is dropped across the internal resistance of the battery. |
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What is the open-circuit voltage of a lead-acid cell? |
2.1 volts. |
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What gases are released when a leas-acid battery is being charged? |
Hydrogen and oxygen. |
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What precautions should be taken in the maintenance shop where both lead-acid and nickel-cadmium batteries are serviced? |
The two types of batteries should be kept separate, and the tools used on one type should not be used on the other. |
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What is the electrolyte used in nickel-cadmium battery? |
Potassium hydroxide and water. |
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Why is a hydrometer not used to measure the state of charge of a nickel-cadmium battery? |
The electrolyte of a nickel-cadmium battery does not enter into the chemical changes that occur when the battery is changed or discharged. |
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Is the electrolyte level of a nickel-cadmium battery lowest when the battery is fully charged or fully discharged? |
Fully discharged. |
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What is a result of cell imbalance in a nickel-cadmium battery? |
The low internal resistance allows current to flow between the unbalanced cells and generate heat. |
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What is thermal runaway? |
The large current flow allowed by the low internal resistance causes the middle cells to produce more heat than they can dissipate. |
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How can thermal runaway be prevented? |
By carefully monitoring the temperature of the middle cells and controlling the charging current to prevent an excess of the current flowing into the battery. |
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How is it possible to know when a nickel-cadmium battery is fully charged? |
Completely discharge the battery and give it a constant-current charge to 140% of its ampere-hour capacity. |
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What is used to neutralize spilled electrolyte from a nickel-cadmium battery? |
A solution of boric acid and water. |
