Sub Element G5: Electrical Principles

Question 1

What is impedance?

Answer 1

The opposition to the flow of current in an AC circuit

Question 2

What is reactance?

Answer 2

Opposition to the flow of alternating current caused by capacitance or inductance

Question 3

Which of the following causes opposition to the flow of alternating current in an inductor?

Answer 3

Reactance

Question 4

Which of the following causes opposition to the flow of alternating current in a capacitor?

Answer 4

Reactance

Question 5

How does an inductor react to AC?

Answer 5

As the frequency of the applied AC increases, the reactance increases

Question 6

How does a capacitor react to AC?

Answer 6

As the frequency of the applied AC increases, the reactance decreases

Question 7

What happens when the impedance of an electrical load is equal to the output impedance of a power source, assuming both impedances are resistive?

Answer 7

The source can deliver maximum power to the load

Question 8

What is one reason to use an impedance matching transformer?

Answer 8

To maximize the transfer of power

Question 9

What unit is used to measure reactance?

Answer 9

Ohm

Question 10

Which of the following devices can be used for impedance matching at radio frequencies?

Answer 10

A transformer
A Pi-network
A length of transmission line
All these choices are correct

Question 11

Which of the following describes one method of impedance matching between two AC circuits?

Answer 11

Insert an LC network between the two circuits

Question 12

What dB change represents a factor of two increase or decrease in power?

Answer 12

Approximately 3 dB

Question 13

How does the total current relate to the individual currents in each branch of a purely resistive parallel circuit?

Answer 13

It equals the sum of the currents through each branch

Question 14

How many watts of electrical power are used if 400 VDC is supplied to an 800 ohm load?

Answer 14

200 watts

Question 15

How many watts of electrical power are used by a 12 VDC light bulb that draws 0.2 amperes?

Answer 15

2.4 watts

Question 16

How many watts are dissipated when a current of 7.0 milliamperes flows through a 1250 ohm resistance?

Answer 16

Approximately 61 milliwatts

Question 17

What is the output PEP from a transmitter if an oscilloscope measures 200 volts peak-to-peak across a 50 ohm dummy load connected to the transmitter output?

Answer 17

100 watts

Question 18

What value of an AC signal produces the same power dissipation in a resistor as a DC voltage of the same value?

Answer 18

The RMS value

Question 19

What is the peak-to-peak voltage of a sine wave with an RMS voltage of 120.0 volts?

Answer 19

339.4 volts

Question 20

What is the RMS voltage of a sine wave with a value of 17 volts peak?

Answer 20

12 volts

Question 21

What percentage of power loss would result from a transmission line loss of 1 dB?

Answer 21

20.6 percent

Question 22

What is the ratio of peak envelope power to average power for an unmodulated carrier?

Answer 22

1.00

Question 23

What would be the RMS voltage across a 50 ohm dummy load dissipating 1200 watts?

Answer 23

245 volts

Question 24

What is the output PEP of an unmodulated carrier if an average reading wattmeter connected to the transmitter output indicates 1060 watts?

Answer 24

1060 watts

Question 25

What is the output PEP from a transmitter if an oscilloscope measures 500 volts peak-to-peak across a 50 ohm resistive load connected to the transmitter output?

Answer 25

625 watts

Question 26

What causes a voltage to appear across the secondary winding of a transformer when an AC voltage source is connected across its primary winding?

Answer 26

Mutual inductance

Question 27

What happens if a signal is applied to the secondary winding of a 4:1 voltage step- down transformer instead of the primary winding??

Answer 27

The output voltage is multiplied by 4

Question 28

Which of the following components increases the total resistance of a resistor?

Answer 28

A series resistor

Question 29

What is the total resistance of three 100 ohm resistors in parallel?

Answer 29

33.3 ohms

Question 30

If three equal value resistors in series produce 450 ohms, what is the value of each resistor?

Answer 30

150 ohms

Question 31

What is the RMS voltage across a 500-turn secondary winding in a transformer if the 2250-turn primary is connected to 120 VAC?

Answer 31

26.7 volts

Question 32

What is the turns ratio of a transformer used to match an audio amplifier having 600 ohm output impedance to a speaker having 4 ohm impedance?

Answer 32

12.2 to 1

Question 33

What is the equivalent capacitance of two 5.0 nanofarad capacitors and one 750 picofarad capacitor connected in parallel?

Answer 33

10.750 nanofarads

Question 34

What is the capacitance of three 100 microfarad capacitors connected in series?

Answer 34

33.3 microfarads

Question 35

What is the inductance of three 10 millihenry inductors connected in parallel?

Answer 35

3.3 millihenries

Question 36

What is the inductance of a 20 millihenry inductor connected in series with a 50 millihenry inductor?

Answer 36

70 millihenries

Question 37

What is the capacitance of a 20 microfarad capacitor connected in series with a 50 microfarad capacitor?

Answer 37

14.3 microfarads

Question 38

Which of the following components should be added to a capacitor to increase the capacitance?

Answer 38

A capacitor in parallel

Question 39

Which of the following components should be added to an inductor to increase the inductance?

Answer 39

An inductor in series

Question 40

What is the total resistance of a 10 ohm, a 20 ohm, and a 50 ohm resistor connected in parallel?

Answer 40

5.9 ohms

Question 41

Why is the conductor of the primary winding of many voltage step-up transformers larger in diameter than the conductor of the secondary winding??

Answer 41

To accommodate the higher current of the primary

Question 42

What is the value in nanofarads (nF) of a 22,000 picofarad (pF) capacitor?

Answer 42

22

Question 43

What is the value in microfarads of a 4700 nanofarad (nF) capacitor?

Answer 43

4.7