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Electronics ETA AC Certification
Practice Exam
In alternating current: A. current flow alternates back and forth B. voltage alternates positive and negative C. resistance changes between high and low D. A and B above
- Answer-D. A and B above Historically, DC came before AC because: A. DC is more useful B. DC is easier to transmit over long distances C. AC requires more advanced technology D. AC is less efficient - Answer-C. AC requires more advanced technology An AC voltage source schematic symbol: A. is a sine wave in a circle B. represents an idealized voltage source C. is considered to have zero internal resistance D. all of the above - Answer-D. all of the above The opposition to current flow presented by capacitors and inductors is called: A. Resistance B. Reactance C. Impedance D. Reluctance - Answer-D. Reluctance Impedance is: A. any combination of resistance and reactance B. another name for resistance C. another name for reactance D. measured in watt-hours - Answer-A. any combination of resistance and reactance AC voltage, current, resistance and power are often indicated by: A. lower-case letters B. smaller-type letters C. Greek symbols D. letters in parentheses - Answer-A. lower-case letters The quadrants in a 4-quadrant X-Y graph are: A. 1, 2, 3, 4, clockwise from upper right B. A, B, C, D, clockwise from upper left C. I, II, III, IV, counter-clockwise from upper left D. I, II, III, IV, counter-clockwise from upper right - Answer-D. I, II, III, IV, counter-clockwise from upper right
A phasor is: A. an arrow with a specific magnitude and direction B. often used to represent voltage or current C. considered to be rotating counter-clockwise D. all of the above - Answer-D. all of the above In a right triangle: A. all the internal angles add up to 90O B. one internal angle is 90O C. all the internal angles are the same D. every internal angle is 90O - Answer- D. every internal angle is 90* In the illustration at right, the Opposite, Adjacent and Hypotenuse are, respectively: A. 3,2,1 B. 3,1,2 C. 2,3,1 D. 2,1,3 - Answer-A. 3,2, The sine, cosine and tangent of a right triangle are, respectively: A. Op / Adj, Adj / Op, Hyp / Adj B. Op / Hyp, Adj / Hyp, Op / Adj C. Adj / Op, Adj / Hyp, Op / Hyp D. Hyp / Op, Hyp/ Adj, Op / Adj - Answer-B. Op / Hyp, Adj / Hyp, Op / Adj π is approximately: A. 0.707 B. 6.3 C. 3.14 D. 3.142 - Answer-C. 3. The circumference of a circle is: A. π x radius squared B. π x radius C. π x diameter D. π / diameter - Answer-C. π x diameter A radian: A. is the same length as a radius B. if multiplied by 2π, equal to circumference C. the same length as a diameter D. A and B above - Answer-D. A and B above Angular velocity is: A. the speed of a phasor tip B. the Greek letter ω C. 1 / 2π times frequency D. all of the above - Answer-D. all of the above An imaginary number corresponds to: A. a point on the X-axis to the left of the origin B. a point in quadrant III C. a point on the Y-axis D. a point in quadrant IV - Answer-C. a point on the Y-axis
A ramp is: A. a linear rise or fall in voltage over time B. a signal that gradually rises in amplitude C. a waveform that gradually rises in frequency D. a waveform that gradually rises in harmonic content - Answer-D. a waveform that gradually rises in harmonic content The RMS voltage of a sine wave is the same as the average voltage: A. true B. false
- Answer-B. false An inexpensive AC voltmeter gives an accurate AC voltage reading on the following: A. a 60Hz square wave B. a 20kHz sine wave C. a 60Hz sine wave D. any waveform with a frequency of 60Hz - Answer-C. a 60Hz sine wave The peak voltage of a sine wave is: A. 1.4 times the RMS voltage B. 1.4 times the absolute voltage C. 1.4 times the average voltage D. 0.707 times the RMS voltage - Answer-B. 1.4 times the absolute voltage The peak power of a sine wave is: A. 1.4 times the average power C. twice the average power B. ½ the average power D. 0.707 times the average power - Answer- A. 1.4 times the average power An oscilloscope is most commonly used to display: A. waveform distortion B. the spectrum of a waveform C. a signal waveform in real time D. phase delay of an RC circuit - Answer-C. a signal waveform in real time The vertical size of the waveform on the display is adjusted using: A. the 5X setting B. the trigger threshold knob C. the vertical sensitivity switch D. the vertical position pot - Answer-A. the 5X setting "Triggering" refers to: A. synchronizing the sweep to the waveform B. vertically centering the sweep C. horizontally centering the sweep D. adjusting the horizontal sweep speed - Answer-B. vertically centering the sweep
The time interval displayed in a single sweep is adjusted using: A. the astigmatism control B. the horizontal sweep time switch C. the horizontal position control D. the trigger threshold control - Answer-B. the horizontal sweep time switch The maximum voltage that can be displayed can be increased by: A. using a 10X attenuator probe B. using the X-Y setting C. manually setting the trigger voltage D. buying a better scope - Answer-A. using a 10X attenuator probe Input loading refers to: A. the ratio of probe resistance to scope input resistance in 10X mode B. adjusting the input circuit so it is purely resistive C. selecting which input activates the trigger D. the load placed on the circuit under test by the oscilloscope - Answer-D. the load placed on the circuit under test by the oscilloscope Setting the input switch to "AC": A. adjusts the scope to run on 117VAC power B. causes the scope to display only DC, filtering out any AC at the input C. causes the horizontal sweep circuit to trigger on an AC voltage D. Inserts a capacitor in series with the vertical sensitivity switch - Answer-D. Inserts a capacitor in series with the vertical sensitivity switch The X-Y setting of the sweep time switch: A. exchanges X and Y axes, so the waveform appears vertical B. displays input 1 vs. input 2 as an X-Y graph C. locks horizontal and vertical sensitivity controls so they are always equal D. switches the trigger input from input 1 to input 2 - Answer-B. displays input 1 vs. input 2 as an X- Y graph The best way to connect a scope ground to the ground of the unit under test is: A. via the clip that attaches to the probe B. via a separate wire to the scope chassis C. via the ground pins of the AC plugs of the scope and the unit under test D. the scope and the unit under test do not need to be grounded together. - Answer-B. via a separate wire to the scope chassis An active probe: A. contains an amplifier in the probe B. reduces input loading on the circuit under test C. can easily be damaged D. all of the above - Answer-D. all of the above
White noise contains equal energy in the frequency ranges: A. 300Hz - 700Hz and 1.5kHz - 1.9kHz B. 200Hz - 400Hz and 2kHz - 4kHz C. 1kHz - 3kHz and 1MHz - 3MHz D. 6kHz - 10kHz and 60kHz-60.1kHz - Answer-A. 300Hz - 700Hz and 1.5kHz - 1.9kHz A capacitor stores energy in the form of: A. heat B. an electric charge across conductive plates C. an electric charge across conductive plates and in the insulating dielectric between them D. a flowing current - Answer-C. an electric charge across conductive plates and in the insulating dielectric between them Capacitance is primarily determined by; A. plate size, distance between them, and type of dielectric B. plate size, distance between them, and their conductivity C. physical size of the capacitor D. breakdown voltage of the dielectric - Answer-A. plate size, distance between them, and type of dielectric Proper DC polarity must be observed when using: A. a paper-dielectric capacitor B. an electrolytic capacitor C. a mica capacitor D. a ceramic capacitor - Answer-B. an electrolytic capacitor Moving the plates of a capacitor will result in: A. increased capacitance, increased breakdown voltage B. increased capacitance, decreased breakdown voltage C. decreased capacitance, increased breakdown voltage D. distance between plates does not matter, as long as they don't touch - Answer-B. increased capacitance, decreased breakdown voltage In an axial-lead capacitor: A. one lead comes out each end B. both leads come out the same end C. the leads come out the side of the capacitor D. the leads are pre- bent for insertion into a PC board - Answer-B. both leads come out the same end A trimmer capacitor is: A. used to store large amounts of energy B. frequently used as the tuning means in a radio C. polarized D. a variable cap intended for infrequent adjustment - Answer-D. a variable cap intended for infrequent adjustment
The name and symbol for a capacitor's opposition to current flow are: A. capacitive reactance, XC B. capacitive reluctance, RC C. capacitive impedance, ZC D. capacitive inductance, LC - Answer-A. capacitive reactance, XC AC current through a capacitor is out of step with voltage across it. A. false B. true C. depends on the circuit it's connected into D. depends on the frequency - Answer- B. true An inductor coil stores energy in: A. the wire B. the wire's dielectric insulation C. the magnetic field around the coil D. an inductor does not store energy - Answer-C. the magnetic field around the coil An inductor's magnetic field only exists if: A. the coil is the right shape B. the right core material is used C. current is flowing through the coil D. there are no other inductors nearby - Answer-C. current is flowing through the coil Which core material is equivalent to an air core? A. aluminum B. plastic C. ferrite D. carbon - Answer-B. plastic Which core material/s can suffer from saturation? A. soft iron B. ceramic C. ferrite D. A and C - Answer-D. A and C Laminations are used to: A. reduce the cost of construction B. reduce eddy currents C. reduce size and weight D. improve low frequency response - Answer-B. reduce eddy currents The name and symbol for an inductor's opposition to current flow are: A. inductive reluctance, XL B. inductive reactance, RL C. inductive impedance, ZL D. inductive wavelength, ωL - Answer-B. inductive reactance, RL AC current through an inductor is out of step with the voltage across it. A. false B. true C. depends on the circuit it's connected into D. only at radio frequencies - Answer-B. true
When an AC sine wave is connected across a capacitor: A. current leads voltage by 90O B. voltage leads current by 90O C. current falls with increasing frequency D. phase angle depends on the circuit - Answer-A. current leads voltage by 90* When a capacitor is charged through a resistor, it is considered fully charged in: A. one time constant B. three time constants C. five time constants D. ten time constants - Answer-C. five time constants XC of a 1μfd capacitor at 3kHz is: A. 53Ω B. 33Ω C. 300Ω D. 18.9Ω - Answer-A. 53Ω If a capacitor's XC is 9Ω at 10kHz, at 20kHz it will be: A. 18Ω B. 4.5Ω C. 12.6Ω D. 57Ω - Answer-B. 4.5Ω If the XC of an 0.01mfd capacitor is 4kΩ at a certain frequency, XC of an 0.02mfd capacitor at the same frequency will be: A. 8kiΩ B. 5.6kΩ C. 2kΩ D. 2.8kΩ - Answer- C. 2kΩ The formula that describes the voltage/current relationship in an inductor is: A. dT/dI = V/L B. dI/dT = V/L C. dV/dT = I/L D. dL/dT = V/I - Answer-B. dI/dT = V/L The time constant formula is: A. T = RL B. T = RL2 C. T = R / L D. T = R + L - Answer-A. T = RL The property that keeps current from rising instantly when voltage is applied is: A. back emf B. residual magnetism C. mutual inductance D. mutual resistance - Answer-A. back emf A flyback is: A. a magnetized inductor's tendency to attract iron objects B. physical vibration of a coil due to self-induction C. a voltage in an inductor coil induced by an external magnetic field D. a voltage transient generated when a current-carrying inductor is disconnected - Answer-D. a voltage transient generated when a current- carrying inductor is disconnected
When inductors are connected in parallel: A. inductance rises, XL falls B. XL rises, inductance falls C. inductance and XL both fall D. inductance and XL both rise - Answer-C. inductance and XL both fall When an AC sine wave is connected across an inductor: A. voltage lags current by 90 B. saturation lags voltage by 90O C. the magnetic field and current are 90O out of phase D. current lags voltage by 90O - Answer-D. current lags voltage by 90* When an inductor is connected to a DC voltage source through a resistor, current reaches essentially its final value in: A. current continues to rise forever B. one time constant C. three time constants D. five time constants - Answer-D. five time constants XL of a 1mH inductor at 2kHz is: A. 12.6 x 106W B. 12.6kW C. 12.6Ω D. 8Ω - Answer- C. 12.6Ω If an inductor has an XL of 50Ω at a 1kHz, XL at 2kHz will be: A. 25Ω B. 35Ω C. 100Ω D. 71Ω - Answer-C. 100Ω The step up/step down ratio is determined by: A. the ratio of wire gauge in the primary to wire gauge in the secondary B. the turns ratio C. the impedance ratio D. the ratio of the diameters of the coils - Answer-B. the turns ratio In a 5:1 transformer, if the load on the secondary is 3A, what is the load on the voltage source? A. 15A B. 0.6A C. 1A D. 0.12A - Answer-B. 0.6A If the voltage across a secondary is 18V and it has a tap 1/3 of the way from one end of the winding, voltage between the tap and that end will be: A. 6V B. 9V C. 1.7V D. 3V - Answer-A. 6V
