Aviation General III - Midterm Review

If three resistors of 3 ohms, 5 ohms, and 22 ohms are connected in series in a 28-volt circuit, how much current will flow through the 3-ohm resistor?

0.93 ampere. In a series circuit, the total resistance is the sum of the individual resistances. In this circuit, the total resistance is 30 ohms. All of the current flows through each resistor. Therefore, the current through each resistor is 0.93 amp. I = E ÷ R = 28 ÷ 3 + 5 + 22 = 28 ÷ 30 = 0.933 amp -or- R= 30 E= 28 I= 28/30 = 0.9333333

A 12-volt electric motor has 1,000 watts input and 1 horsepower output. Maintaining the same efficiency, how much input power will a 24-volt, 1-horsepower electric motor require?(Note: 1 horsepower = 746 watts)

1,000 watts. The power produced by an electric motor is the product of its voltage and its current. A 12-volt motor will require 83.3 amps of current for its 1,000 watts of input power to produce 746 watts (1 horsepower) of output power. A 24-volt motor operating at the same efficiency will also require 1,000 watts of input power for its 746 watts of output power, but it will need only 41.7 amps of current.

(Refer to Figure 13.) Determine the current flow in circuit.

1.4 amps The total resistance of this circuit is 8.57 ohms. The total current flowing in this circuit is 1.4 amps.

(Refer to Figure 8.) With an ohmmeter connected into the circuit as shown, what will the ohmmeter read?

10 ohms The ohmmeter will read the resistance of R(1) and R(2) in parallel; this is 10 ohms. The open circuit (break) in resistor R(3) gives it an infinite resistance, and it does not affect the reading of the ohmmeter.

A circuit has an applied voltage of 30 volts and a load consisting of a 10-ohm resistor in series with a 20-ohm resistor. What is the voltage drop across the 10-ohm resistor?

10 volts. In a series circuit, the voltage drop across each resistor is determined by its resistance. In this circuit, the total resistance is 30 ohms, and the total voltage is 30 volts. One amp of current flows through each resistor and this gives a 10-volt drop across the 10-ohm resistor. E = I x R = 1 x 10 = 10 volts

(Refer to Figure 14.) The total resistance of the circuit is R1 = 5 R2 = 4 R3 =6 R4 =12 R5 =10 R2, R3, and R4 are in parallel R1, R234, and R5 are in Series

17ohms The total resistance can be found in two steps: 1. Combine resistances R(2), R(3), and R(4) in parallel. 2. Combine resistances R(1), R(2-3-4), and R(5) in series.

(Refer to Figure 21.) Which symbol represents a variable resistor? Symbol 1 - Resistor with line coming from middle Symbol 2 - Resistor with arrow through it Symbol 3 - Resistor with line coming from top-right and bottom-left Resistor- zigzag line

2 Symbol 2 is a variable resistor (rheostat). This is not the most widely used symbol as it can be used only for a rheostat (a variable resistor with only two connections) and not for a potentiometer. Symbol 1 is a tapped resistor. Symbol 3 is a tapped resistor -- tapped at two places.

(Refer to Figure 4.) How much power is being furnished to the circuit? R= 5 ohms I = 23 amps

2,645 watts This is a resistive circuit. The power is the product of the square of the current times the resistance. P = I^2 x R = 23^2 x 5 = 2,645 watts -or- E=I x R E= 115 P= I x E P =2,645

.002 kV equals

2.0 volts One kilovolt (kV) is 1,000 volts. Two thousandths (.002) of a kilovolt is equal to 2.0 volts.

(Refer to Figure 12.) Find the total resistance in the circuit. R1=18 R2=12 R3=4 R4=12 R5=6

21.2 ohms. This problem can be solved in four steps: 1. Combine resistors R(4) and R(5) in parallel. 2. Combine resistor R(2) with R(4-5) in series. 3. Combine resistors R(2-4-5) with R(3) in parallel. 4. Combine resistors R(2-3-4-5) with R(1) in series.

(Refer to Figure 64.) A 24-volt source is required to furnish 48 watts to a parallel circuit consisting of two resistors of equal value. What is the value of each resistor? R(t) = E^2/P

24 ohms To solve this problem, first find the total resistance of the circuit. R(T) = E^2 ÷ P = 24^2 ÷ 48 = 12 ohms There are two resistors of equal value in parallel that provide this resistance, therefore each resistor must have a resistance of twice this value, or 24 ohms.

In a parallel circuit with four 6-ohm resistors across a 24-volt battery, what is the total voltage across resistor-three (VR3) in the circuit?

24 volts. In a parallel circuit the source or battery voltage is applied to each of the individual resistors.

A 24-volt source is required to furnish 48 watts to a parallel circuit consisting of four resistors of equal value. What is the voltage drop across each resistor?

24 volts. Since the resistors are all in parallel across the 24-volt power source, each resistor has the entire 24 volts dropped across it.

(Refer to Figure 11.) Find the voltage across the 8-ohm resistor

24 volts. The 8-ohm resistor, R(1), is across the full 24 volts of the battery.

How many amperes will a 28-volt generator be required to supply to a circuit containing five lamps in parallel, three of which have a resistance of 6 ohms each and two of which have a resistance of 5 ohms each?

25.23 amperes A current of 4.67 amps flows through each of the three six-ohm lamps. And a current of 5.6 amps flows through each of the 5-ohm lamps. Since all of these lamps are in parallel, the total current is the sum of the currents flowing through each lamp. The total current is 25.21 amps.

What is the operating resistance of a 30-watt light bulb designed for a 28-volt system?

26 ohms A 30-watt light bulb operating in a 28-volt electrical system has a hot resistance (operating resistance) of 26.13 ohms. R = E^2 ÷ P = 28^2 ÷ 30 = 26.12 omega

(Refer to figure 17) Which of the components is a potentiometer?

3 The component identified as 3 is a potentiometer. The component identified as 5 is a variable capacitor. The component identified as 11 is an inductor (choke).

(Refer to Figure 6.) If resistor R(5) is disconnected at the junction of R(4) and R(3) as shown, what will the ohmmeter read? R1=12 R2=6 R3=6 R4=6 R5= Disconnected R3 and 4 are series R1, R2, and R34 are parallel

3 ohms With resistor R(5) disconnected, the ohmmeter reads the parallel resistance of R(1) and R(2) in parallel with R(4) and R(3), which are in series. The total resistance is found by the formula: Rp = 1 / [1/R1 + 1/R2 + 1/(R3 + R4)] = 1 / [1/12 + 1/6 + 1/(6 + 6)] = 3 ohms.

(Refer to Figure 11.) Find the total current flowing in the wire between points C and D.

3.0 amperes The total resistance between points D-E and G-H is 8 ohms. This is the resistance of resistors R(2) and R(3) in parallel. There is a voltage of 24 volts across these two parallel resistors, so the current through the line between C and D is three amps.

(Refer to Figure 10.) What is the measured voltage of the series-parallel circuit between terminals A and B?

3.0 volts. The two batteries on the left side are connected in series, and the two batteries on the right side are connected in series. The two pairs of batteries are connected in parallel. The series connections between terminals A and B give this circuit a voltage of 3.0 volts.

(Refer to Figure 64.) A 48-volt source is required to furnish 192 watts to a parallel circuit consisting of three resistors of equal value. What is the value of each resistor? R_t = E^2/P

36 ohms. The total resistance needed to dissipate 192 watts of electrical power from a 48-volt source is 12 ohms. R(T) = E^2 ÷ P = 48^2 ÷ 192 = 12 omega Since three resistors in parallel give 12 ohms, each resistor must have a resistance three times this value. R = R(T) x n = 12 x 3 = 36

How much power must a 24-volt generator furnish to a system which contains the following loads?UNIT RATING One motor (75 percent efficient) 1/5 hp Three position lights 20 watts each One heating element 5 amp One anticollision light 3 amp (Note: 1 horsepower = 746 watts)

450 watts. The motor is 1/5 hp, therefore 746 watts (1 hp) ÷ 5 = 149 watts. This is the output of the engine. It takes more energy to produce 149 watts -- find this with the efficiency rating, 149/X = 75/100; X = 199. Therefore, the 1/5 horsepower motor that is 75 percent efficient requires 199 watts. The three position lights require a total of 60 watts. The heating element requires 120 watts. The anticollision light requires 72 watts. The total power the generator must produce is 451 watts.

In a parallel circuit with three 6-ohm resistors across a 12-volt battery, what is the total current (It) value in the circuit?

6 amps The total resistance of this circuit is 2 ohms. The total current flowing in this circuit is 6 amps.

A 24-volt, 1-horsepower DC electric motor that is 80 percent efficient requires 932.5 watts. How much power will a 12-volt, 1-horsepower DC electric motor that is 75 percent efficient require?(Note: 1 horsepower = 746 watts)

994.6 watts. When we know the horsepower output and the efficiency of an electric motor, the voltage does not enter into the computation. To find the number of watts required, divide the wattage for the total horsepower by the decimal equivalent of the efficiency. 746 ÷ 0.75 = 994.6 watts

Which requires the most electrical power?(Note: 1 horsepower = 746 watts) -A 1/5-horsepower, 24-volt motor which is 75 percent efficient. -Four 30-watt lamps arranged in a 12-volt parallel circuit. -A 24-volt anticollision light circuit consisting of two light assemblies which require 3 amperes each during operation.

A 1/5-horsepower, 24-volt motor which is 75 percent efficient. The 1/5-horsepower motor operating at 75 percent efficiency uses 198.93 watts of power. The four 30-watt lamps use 120 watts of power. The anticollision light circuit uses 144 watts of power.

A 14-ohm resistor is to be installed in a series circuit carrying .05 ampere. How much power will the resistor be required to dissipate?

At least 35 milliwatts. Power dissipated in a resistor is found by multiplying its resistance by the square of the current. P = I^2 x R = 0.05^2 x 14 = 0.035 watts. 0.035 watts is 35 milliwatts.

What is the basic unit of electrical quantity?

Coulomb The coulomb is the basic unit of electrical quantity. One coulomb is equal to 6.28 X 10^18 electrons.

What does the letter Q symbolize when measuring electrical charge?

Coulomb. The general formula for capacitance in terms of charge and voltage is C = Q/E, where: C = Capacitance measured in farads E = Applied voltage measured in volts Q = Charge measured in coulombs.

Which of these will cause the resistance of a conductor to decrease?

Decrease the length or increase the cross-sectional area. The resistance of a conductor varies directly as its length, inversely as its cross-sectional area, and directly with the resistivity of its material. Either decreasing the length or increasing the cross-sectional area of a conductor will cause its resistance to decrease.

Which of the following are commonly used as a rectifier in electrical circuits?

Diodes Diodes are two element electronic components that act as electron check valves. They allow electrons to pass freely in one direction but block their flow in the opposite direction. They are used as rectifiers in electrical circuits.

Which is correct in reference to electrical resistance? -Two electrical devices will have the same combined resistance if they are connected in series as they will have if connected in parallel. -If one of three bulbs in a parallel lighting circuit is removed, the total resistance of the circuit will become greater. -An electrical device that has a high resistance will use more power than one with a low resistance with the same applied voltage.

If one of three bulbs in a parallel lighting circuit is removed, the total resistance of the circuit will become greater. In a parallel electrical circuit, each bulb provides a path for current to flow. The more paths there are, the less the circuit resistance will be. When one bulb is removed, the circuit resistance increases.

(Refer to Figure 7.) If resistor R(3) is disconnected at terminal D, what will the ohmmeter read?

Infinite resistance When resistor R(3) is disconnected at terminal D, it is isolated from the rest of the circuit, and the ohmmeter will read only the resistance of R(3). Because R(3) is open (it has a break in it), its resistance is infinite.

Through which material will magnetic lines of force pass the most readily? -Copper. -Iron. -Aluminum.

Iron. The permeability of a material is a measure of the ease with which lines of magnetic force can pass through it. Iron has the highest permeability of all the metals listed in this question.

Which term means .001 ampere?

Milliampere. The metric prefix 'milli-' means one thousandth. 0.001 ampere is one milliampere.

Which effect does not apply to the movement of electrons flowing in a conductor? -Magnetic energy. -Thermal energy. -Static energy.

Static energy. Current flowing through a conductor produces a magnetic field and also dissipates thermal energy.

When referring to an electrical circuit diagram, what point is considered to be at zero voltage?

The ground reference The ground reference, shown on a schematic diagram as a triangular-shaped series of parallel lines, is the point considered to be at zero voltage. All voltages, both positive and negative, are measured from this ground reference.

When referencing resistance in a parallel DC circuit, which of the following statements is true? -The current is equal in all portions of the circuit. -The total current is equal to the sum of the currents through the individual branches of the circuit. -The current in amperes can be found by dividing the source voltage in volts by the sum of the resistors in ohms.

The total current is equal to the sum of the currents through the individual branches of the circuit. According to Kirchhoff's current law, the current flowing in a parallel circuit is equal to the sum of the currents flowing through each of the individual branches of the circuit.

What is the purpose of the ground symbol used in electrical circuit diagrams?

To show that there is a return path for the current between the source of electrical energy and the load. The ground symbol used on electrical schematic diagrams indicates that there is a return path for the current between the source of electrical energy and the load.

Which is correct concerning a parallel circuit? -Total resistance will be smaller than the smallest resistor. -Total resistance will decrease when one of the resistances is removed. -Total voltage drop is the same as the total resistance.

Total resistance will be smaller than the smallest resistor. In a parallel circuit each resistor forms a path for the current to follow and the total resistance is always smaller than that of the smallest resistor.

Which requires the most electrical power during operation? (Note: 1 horsepower = 746 watts)

Two lights requiring 3 amperes each in a 24-volt parallel system The 12-volt motor requires 96 watts of power. The four 30-watt lamps require 120 watts of power. The two 24-volt, 3-amp lights require 144 watts of power.

(Refer to Figure 9.) How many instruments (voltmeters and ammeters) are installed correctly?

Two. The first ammeter is installed across the voltage. This is wrong; the ammeter will burn out. The first voltmeter will measure the source voltage (the voltage of the battery), but its polarity is wrong. It will read backward. The voltmeter across the light bulb is installed correctly. The ammeter in series with the light bulb and the battery is correct. It will read the current flowing through the light bulb.

The potential difference between two conductors which are insulated from each other is measured in

Volts The potential difference between two conductors is a measure of the electrical pressure difference between the conductors. Electrical pressure is measured in volts.

What unit is used to express electrical power?

Watt. A watt is a measure of electrical power. A volt is a measure of electrical pressure. An ampere is a measure of electrical current flow.

What will a voltmeter read if properly connected across a closed switch in a circuit with electrical power on?

Zero voltage When a voltmeter is connected across a closed switch in perfect condition or a good fuse, it will read zero voltage. A voltage drop of up to 0.2 volts is acceptable with maximum circuit current flow through the switch.

(Refer to Figure 17.) The electrical symbol represented at number 5 is a variable

capacitor A variable capacitor is shown by symbol 5. An inductor is shown by symbol 11. A variable resistor (potentiometer) is shown by symbol 3.

A cabin entry light of 10 watts and a dome light of 20 watts are connected in parallel to a 30-volt source. If the voltage across the 10-watt light is measured, it will be

equal to the voltage across the 20-watt light. When lights are connected in parallel across a voltage source, the voltage across each of the lights will be the same as the voltage of the source.

The correct way to connect a test voltmeter in a circuit is

in parallel with a unit. A voltmeter must always be connected in a circuit in parallel with the unit whose voltage is to be measured.

Convert farads to picofarads by:

multiplying farads by 10 to the power of 12 One farad is equal to 10^12 picofarads. Example: 2 farads is equal to 2 x 10^12 (2,000,000,000) picofarads.

Convert farads to microfarads by

multiplying farads by 10 to the power of 6 One farad is equal to 10^6 microfarads. Example: 2 farads is equal to 2 x 10^6 (2,000,000) microfarads.

A thermal switch, or thermal protector, as used in an electric motor, is designed to

open the circuit in order to allow cooling of the motor. A thermal switch is another name for a built-in thermal circuit breaker. This is a circuit protection device that opens the circuit when the windings of the motor get too hot. If the motor overheats for any reason, the thermal switch will open the power circuit to the motor and allow the motor to cool.

(Refer to Figure 20.) Troubleshooting an open circuit with a voltmeter as shown in this circuit will

permit the battery voltage to appear on the voltmeter. An open in the resistor will cause an infinite resistance. No current can flow in the circuit. Since no current flows, there is no voltage drop across the switch or the lamp, and the entire battery voltage is read on the voltmeter.

Diodes are used in electrical power supply circuits primarily as

rectifiers. A diode (either a semiconductor diode or an electron-tube diode) is an electron check valve. A diode allows electrons to pass in one direction, but blocks their flow in the reverse direction. This is the action of a rectifier.

Capacitors are sometimes used in DC circuits to

smooth out slight pulsations in current/voltage. Capacitors store electrical charges and are sometimes used in DC circuits to smooth out slight pulsations in current or voltage. Capacitors accept electrons when there is an excess and release them back into the circuit when the values decrease.

The voltage drop in a circuit of known resistance is dependent on

the amperage of the circuit. The voltage drop across a circuit is determined by two things: the resistance of the conductor and the amount of current flowing through it (the amperage). In this question, the resistance of the circuit is fixed; therefore, the voltage drop is determined by the amperage in the circuit.