Q. No.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) |
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| (c) | (d) |
| 1. | (a) and (d) |
| 2. | (a), (b), (c), and (d) |
| 3. | (a) and (b) |
| 4. | only (a) |
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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. A
2. 14 A
3. 10 A
4. 15 A
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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 |
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A direct current of \(5~ A\) is superimposed on an alternating current \(I=10sin ~\omega t\) flowing through a wire. The effective value of the resulting current will be:
| 1. | \(15/2~A\) | 2. | \(5 \sqrt{3}~A\) |
| 3. | \(5 \sqrt{5}~A\) | 4. | \(15~A\) |
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 |
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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. \( \frac{1}{2}\left(i_1^2+i_2^2\right)^{1 / 2}\)
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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. |
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The time required for a 50 Hz sinusoidal alternating current to change its value from zero to the r.m.s. value will be:
1.
2.
3.
4.
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The output current versus time curve of a rectifier is shown in the figure.
The average value of the output current in this case will be:
| 1. | 0 | 2. | \(I_0 \over 2\) |
| 3. | \(2I_0 \over \pi\) | 4. | \(I_0\) |
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