Select Chapter Topics: The variation of EMF with time for four types of generators is shown in the figures. Which amongst them can be called AC voltage?  (a) (b)  (c) (d)

 1 (a) and (d) 2 (a), (b), (c), and (d) 3 (a) and (b) 4 only (a)  Subtopic:  AC vs DC |
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In the diagram, two sinusoidal voltages of the same frequency are shown. What is the frequency and the phase relationship between the voltages? Frequency in Hz Phase lead of N over M in radians 1. 0.4 –π/4 2. 2.5 –π/2 3. 2.5 +π/2 4. 2.5 –π/4  Subtopic:  AC vs DC |
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An AC ammeter is used to measure the current in a circuit. When a given direct current passes through the circuit, the ac ammeter reads 6 A. When another alternating current passes through the circuit, the AC ammeter reads 8 A. Then the reading of this ammeter if DC and AC flow through the circuit simultaneously is:

1. $10\sqrt{2}$ A

2. 14 A

3. 10 A

4. 15 A  Subtopic:  AC vs DC |
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Alternating current cannot be measured by a D.C. ammeter because:

 1 A.C. cannot pass through D.C. Ammeter 2 A. C. changes direction 3 Average value of current for the complete cycle is zero 4 D.C. Ammeter will get damaged  Subtopic:  AC vs DC |
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In a heating arrangement, an alternating current having a peak value of $$28~\mathrm{A}$$ is used. To produce the same heat energy, if direct current is used to produce the same amount of heat, then its magnitude will be:
1. about $$14~\mathrm{A}$$
2. about $$28~\mathrm{A}$$
3. about $$20~\mathrm{A}$$
4. cannot say  Subtopic:  AC vs DC |
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A generator produces a voltage that is given by V = 240 sin 120 t, where t is in seconds. The frequency and r.m.s. voltage are:

 1 60 Hz and 240 V 2 19 Hz and 120 V 3 19 Hz and 170 V 4 754 Hz and 70 V  Subtopic:  RMS & Average Values |
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An alternating current is given as i = icos $$\omega t$$ - isin $$\omega t$$. The value of rms current is given by:
1. $$\frac{1}{\sqrt{2}}\left(i_1+i_2\right)$$
2. $$\frac{1}{\sqrt{2}}\left(i_i+i_2\right)^2$$
3. $$\frac{1}{\sqrt{2}}\left(i_1^2+i_2^2\right)^{1 / 2}$$
4. $$\frac{1}{2}\left(i_1^2+i_2^2\right)^{1 / 2}$$  Subtopic:  RMS & Average Values |
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The peak value of an alternating e.m.f. $\mathrm{E}={\mathrm{E}}_{0}$  is 10 volts and its frequency is 50 Hz. At a time $$t=\frac{1}{600}~s,$$ the instantaneous value of the e.m.f. will be:

1. 1 volt

2. $5\sqrt{3}$ volts

3. 5 volts

4. 10 volts  Subtopic:  RMS & Average Values |
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The variation of the instantaneous current (I) and the instantaneous emf (E) in a circuit are shown in the figure. Which of the following statements is correct? 1 The voltage lags behind the current by π/2. 2 The voltage leads the current by π/2. 3 The voltage and the current are in phase. 4 The voltage leads the current by π.  Subtopic:  RMS & Average Values |
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When an alternating voltage is given as $$E = (6 sin\omega t - 2 cos \omega t)$$ volt, what is its RMS value?
1. $$4 \sqrt 2$$ V
2. $$2 \sqrt 5$$ V
3. $$2 \sqrt 3$$ V
4. $$4$$ V  Subtopic:  RMS & Average Values |
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