AC Fundamentals – Exercise – 1

46. A sine wave with a period of 4 ms is changing at a faster rate than a sine wave with a period of ________.

(a) 0.0045 s
(b) 2 ms
(c) 1.5 ms
(d) 3,000 μs

Answer
Answer : (a)
Explanation
Explanation :

f = 1/t
Frequencyis indirectly proportional to time.

Q = f = 1/4 ms = 1000/4 = 250
A = f = 1/0.0045 s = 222. 22
B = f = 1/2 ms = 1000/2 = 500
C = f = 1/1.5 ms = 1000/1.5 = 666.66
D = f = 1/3,000 μs = 10,00,000/3000 = 333.33

Here Option A is 4.5 ms which is the larger time period from given options comparing with 4 ms. So, Option A is the correct answer.

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47. When a sine wave has a frequency of 100 Hz in 12 s it goes through ________.

(a) 1/100 cycle
(b) 12 cycles
(c) 120 cycles
(d) 1,200 cycles

Answer
Answer : (d)
Explanation
Explanation :

Frequency measured in cycles per second (cps) or the interchangeable Hertz (Hz).
Example – 60 cps = 60 Hz.

Here, 100 Hz means 100 cycles per second or 100 cycles in 1 second.
So, 100 Hz in 12 s means 100 * 12 = 1,200 cycles in 12 second.

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48. If the peak of a sine wave is 13 V, the peak-to-peak value is ________.

(a) 6.5 V
(b) 13 V
(c) 26 V
(d) none of the above

Answer
Answer : (c)
Explanation
Explanation :

METHOD-1

Peak to peak voltage = 2 * peak voltage = 2 *  13 = 26 V.

METHOD-1

Positive peak is 13v, negative peak is also 13v.
Peak to peak voltage  = Positive peak + Negative peak = 13 V + 13 V = 26 V.

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49. A phasor represents ________.

(a) the magnitude and a quantity direction
(b) the width of a quantity
(c) the phase angle
(d) the magnitude of a quantity

Answer
Answer : (a)
Explanation
Explanation :

The phasor diagram represents both the magnitude and the phase angle between voltage and current.

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50. Two series resistors are connected to an ac source. If there are 7.5 V rms across one resistor and 4.2 V rms across the other, the peak source voltage is ________.

(a) 16.54 V
(b) 1.65 V
(c) 10.60 V
(d) 5.93 V

Answer
Answer : (a)
Explanation
Explanation :

Vrms = Vmax / 1.414
Vmax = Vrms * 1.414 = (v1rms + v2rms) * 1.414 = (7.5 + 4.2) * 1.414 = 16.54 V.

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