A transformer is used to step up the voltage to a power line. If the stepped-up voltage is 10 times the original value, by how much will the power loss in the line decrease?
a. more than 95
b. between 10 and 20
c. between 20 and 95
d. There will be no change since the power into a transformer equals the power out.
[Ques. 2] When two sound waves are out of phase by _____, destructive interference will occur.
a. 90
c. 540
b. 270
d. 720
[Ques. 3] An electric motor produces 2.0 hp in a Vrms = 120 V circuit. What is Irms for this motor? (1 hp = 746 W)
a. 12 A
c. 0.62 A
b. 6.2 A
d. 1.6 A
[Ques. 4] A phase difference of 480 corresponds to what wavelength difference?
a. 3l
c. 3l/4
b. 3l/2
d. 4l/3
[Ques. 5] An electric motor produces 2.0 hp in a Vrms = 120 V circuit. Using 1 hp = 746 W, how long would it take this motor to do 1.0 kWh of work?
a. 0.67 min
c. 1.3 min
b. 0.67 h
d. 1.3 h
[Ques. 6] The air in a pipe resonates at 150 Hz and 750 Hz, one of these resonances being the fundamental. If the pipe is open at both ends, how many resonances are between the two given ones, and if the pipe is closed at one end, how many resonances are between the two given ones?
a. open: 3; closed: 1
c. open: 2; closed: 0
b. open: 1; closed: 3
d. open: 0; closed: 2
[Ques. 7] An ideal transformer is one that:
a. has an output frequency of 60 Hz.
c. experiences no power loss.
b. has a turn ratio, N2/N1, equal to 1.
d. works with direct current.
[Ques. 8] If the air temperature decreases, how does the resonant frequency in a pipe closed at one end change?
a. It increases.
b. It decreases.
c. It doesn't change since one end of the pipe is closed. d. It doesn't change because resonance is a pressure phenomenon.
[Ques. 9] A transformer is to be designed to increase the 30 kV (rms) output of a generator to the transmission line voltage of 345 kV (rms). If the primary winding has 60 turns, how many turns must the secondary have?
a. 57
c. 690
b. 6900
d. 11
[Ques. 10] A sound intensity of 70 dB is observed at a distance d from the source of sound. What sound intensity would be observed at a distance 2d from the source?
a. 68 dB
c. 64 dB
b. 67 dB
d. 62 dB
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