# A transformer has 100 turns in the primary coil and carries 8 A current. If input power is one kilowatt, the number of turns required in the secondary coil to have 500V output will be  (1) 100 (2) 200 (3) 400 (4) 300

Subtopic:  Transformer |
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The potential difference V and the current i flowing through an instrument in an ac circuit of frequency f are given by $V=5\mathrm{cos}\omega \text{\hspace{0.17em}}t$ volts and I = 2 sin ωt amperes (where ω = 2πf). The power dissipated in the instrument is

(1) Zero

(2) 10 W

(3) 5 W

(4) 2.5 W

Subtopic:  Different Types of AC Circuits |
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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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The peak value of an alternating e.m.f. E is given by $E={E}_{0}\mathrm{cos}\omega \text{\hspace{0.17em}}t$ is 10 volts and its frequency is 50 Hz. At time $t=\frac{1}{600}sec$, the instantaneous e.m.f. is

1. 10 V

2. $5\sqrt{3}\text{\hspace{0.17em}}V$

3. 5 V

4. 1 V

Subtopic:  Different Types of AC Circuits |
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If a current I given by ${I}_{0}\mathrm{sin}\text{\hspace{0.17em}}\left(\omega \text{\hspace{0.17em}}t-\frac{\pi }{2}\right)$ flows in an ac circuit across which an ac potential of $E={E}_{0}\mathrm{sin}\omega \text{\hspace{0.17em}}t$ has been applied, then the power consumption P in the circuit will be

(1) $P=\frac{{E}_{0}{I}_{0}}{\sqrt{2}}$

(2) $P=\sqrt{2}{E}_{0}{I}_{0}$

(3) $P=\frac{{E}_{0}{I}_{0}}{2}$

(4) P = 0

Subtopic:  Different Types of AC Circuits |
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A resistance of $$20~ \Omega$$ is connected to a source of an alternating potential, $$V=220\sin(100 \pi t).$$ The time taken by the current to change from its peak value to its rms value will be:
 1 $$0.2~\text{sec}$$ 2 $$0.25~\text{sec}$$ 3 $$25 \times10^{-3}~\text{sec}$$ 4 $$2.5 \times10^{-3}~\text{sec}$$
Subtopic:  RMS & Average Values |
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An alternating current of frequency $$f$$ is flowing in a circuit containing a resistance $$R$$ and a choke $$L$$ in series. The impedance of this circuit will be:
1. $$R + 2\pi f L$$
2. $$\sqrt{R^{2} + 4 \pi^{2} f^{2} L^{2}}$$
3. $$\sqrt{R^{2} + L^{2}}$$
4. $$\sqrt{R^{2} + 2 \pi f L}$$
Subtopic:  Different Types of AC Circuits |
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A resistance of $$300~\Omega$$ and an inductance of $$\frac{1}{\pi}$$ henry are connected in series to an AC voltage of $$20$$ volts and a $$200$$ Hz frequency. The phase angle between the voltage and current will be:

 1 $$\tan^{- 1} \dfrac{4}{3}$$ 2 $$\tan^{- 1} \dfrac{3}{4}$$ 3 $$\tan^{- 1} \dfrac{3}{2}$$ 4 $$\tan^{- 1} \dfrac{2}{5}$$
Subtopic:  Different Types of AC Circuits |
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In a region of uniform magnetic induction B = 10–2 tesla, a circular coil of radius 30 cm and resistance π2 ohm is rotated about an axis that is perpendicular to the direction of B and which forms a diameter of the coil. If the coil rotates at 200 rpm the amplitude of the alternating current induced in the coil is :

(1) 4π2 mA

(2) 30 mA

(3) 6 mA

(4) 200 mA

Subtopic:  Different Types of AC Circuits |
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In a LCR circuit having L = 8.0 henry, C = 0.5 μF and R = 100 ohm in series. The resonance frequency in radian per second is

(2) 600 Hz