A series LCR AC circuit is at resonance. It contains a resistor of 16 W, a capacitor of 0.35 mF, and an inductor of 90 mH. If an effective (rms) voltage of 150 V is applied, what is the effective (rms) current when the circuit is in resonance?
a. 9.4 A
c. 5.0 A
b. 3.3 A
d. 16.1 A
[Ques. 2] If I0 = 10-12 W/m2 is the threshold of hearing, a sound with intensity I1 = 10-10 W/m2 will give a certain decibel level. Suppose a new sound has an intensity I2 = I12/I0 . What is the new decibel level?
a. 40
c. 10,000
b. 20
d. It will square the decibel level.
[Ques. 3] An AC series circuit contains a resistor of 20 W, a capacitor of 0.75 mF, and an inductor of 80 mH. What frequency should be used to create a resonance condition in the circuit?
a. 650 Hz
c. 160 Hz
b. 530 Hz
d. 320 Hz
[Ques. 4] If one-half of the members of a symphony orchestra are absent because of head colds, thus reducing the overall intensity of sound by 50, what will be the reduction in the decibel level?
a. 5 dB
c. 48 dB
b. 3 dB
d. 1.7 dB
[Ques. 5] In an LCR series circuit with XL > XC, the phase angle between the current and voltage phasors is 30. If the AC frequency doubles, what is the magnitude of the resulting phase angle?
a. 30
b. less than 30
c. more than 30
d. Additional information is needed to reach a determination.
[Ques. 6] What is the intensity of a sound with a measured intensity level of 84 dB? (I0 = 10-12 W/m2)
a. 8.4 10-3 W/m2
c. 2.5 10-5 W/m2
b. 2.5 10-4 W/m2
d. 7.4 10-4 W/m2
[Ques. 7] In an LCR series circuit the capacitive reactance is 24 W. If the AC frequency halves, what will be the resulting capacitive reactance?
a. 24 W
b. 48 W
c. 12 W
d. Additional information is need to find the value.
[Ques. 8] What is the intensity level of a sound with intensity of 5.0 10-11 W/m2? (I0 = 10-12 W/m2)
a. 74 dB
c. 17 dB
b. 54 dB
d. 27 dB
[Ques. 9] A series circuit has equal values for resistance, capacitive reactance, and inductive reactance. The phase angle for this circuit is:
a. 180.
c. 60.
b. 60.
d. not given.
[Ques. 10] Doubling the power output from a speaker emitting a single frequency will result in what increase in loudness?
a. 0.33 dB
c. 4.8 dB
b. 3.0 dB
d. 9.0 dB
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