1160 Practice Exam #3
12) The unit used to measure inductive reactance is: A) the ohm. B) the farad. C) the henry. D) the reluctance.
A
15) Capacitors are connected in parallel to: A) obtain a greater total capacitance than is available in one unit. B) enable the group of capacitors to withstand a higher voltage than any individual capacitor. C) increase the voltage of the circuit. D) increase the resistance of the circuit.
A
19) In a 60 Hz circuit, containing a 12 µF capacitor, the capacitive reactance is ________ ohms. A) 221 B) 720 C) 0.2 D) 0.002
A
24) Transformers are normally rated in A) VA. B) VAR. C) Watt. D) Ohm.
A
14) The insulating material used in a capacitor is called the A) foil. B) dielectric. C) anode. D) cathode
B
23) If the nameplate of a transformer shows the primary rated at 120 volts and the secondary rated at 12 volts then the ________ is 10 to 1. A) power ratio B) turns ratio C) voltage ratio D) both B and C
D
2) When a capacitor is being charged, a current flows through the dielectric of the capacitor. True or False
F
4) The winding of a transformer that receives current from the supply is the secondary winding True or False
F
1) An AC voltage across a pure resistance reaches its peak value at the same instance that the current through the resistance reaches its peak value. True or False
T
3) Capacitors are rated for both capacitance and voltage. True or False
T
5) The frequency of the output of a transformer is always equal to the frequency of the input. True or False
T
6) When a DC inductive circuit is turned off, the inductor's cemf can be much greater than the DC source voltage. True or False
T
7) In a parallel circuit, LT is always less than L1 or L2. True or False
T
8) The load current of a step-up transformer is always less than the primary current. True or False
T
in a 60hz circuit, containing a 12uF capacitor, the capacitive reactance is _____ ohms. A) 221 B) 720 C) 0.2 D) 0.002
A [10^6/(6.28)(60Hz)(12uF)]
17) As frequency increases, XC A) increases. B) decreases. C) remains the same. D) changes direction.
B
18) A 10-µF capacitor is connected to a 110 VAC 60-Hz voltage source, with an ammeter in series. What would the AC current value of the ammeter be? A) 0.202 A B) 0.415 A C) 0.626 A D) 0.838 A
B
22) Autotransformers are transformers that use a ________ winding for the primary and secondary. A) separate B) common C) variable D) fixed
B
9) A transformer is a device used to: A) rectify voltages from AC to DC. B) transfer electric energy by mutual induction. C) convert mechanical energy into electric energy. D) All of the answers are correct.
B
A transformer has a 240V primary and a 60V secondary, With a 5-ohm load connected what is the primary current. A) 12A B) 3A C) 0.75A D) 48A
B [720W/240V= 3A] [60v/5=12A] [(12A)(60V)= 720W]
10) Inductors store energy in the form of: A) current. B) voltage. C) a magnetic field. D) an electric field.
C
16) The ________ capacitor provides more capacitance for a given size than does any other type of capacitor. A) film capacitor B) Mylar C) electrolytic D) ceramic
C
20) Transformer cores are laminated to minimize ________ currents. A) primary B) secondary C) eddy D) stray
C
21) A step-down transformer is used to change: A) high power to low power. B) alternating current to direct current. C) high voltage to low voltage. D) high current to low current.
C
11) Lenz's law states that the induced voltage always acts in a direction to ________ the current change that produced it. A) divert B) invert C) aid D) oppose
D
13) In a pure inductive circuit the power in watts is equal to A) voltage × current. B) inductance × current. C) inductance × voltage. D) zero.
D