In a step-up transformer, the turn ratio is 1:2. A Leclanche cell (e.m.f. 1.5V) is connected across the primary coil. The voltage developed in the secondary coil would be-

1. 3.0 V

2. 0.75 V

3. 1.5 V

4. Zero

A 220 V, 50 Hz ac source is connected to an inductance of 0.2 H and a resistance of 20 ohms in series. What is the current in the circuit :

1.  10A

2.  5A

3.  33.3A

4.  3.33A

$\mathrm{If} {\mathrm{X}}_{\mathrm{L}} = {\mathrm{X}}_{\mathrm{C}} \mathrm{then} \mathrm{the} \mathrm{reading} \mathrm{of} \mathrm{ideal} \mathrm{voltmeter} \mathrm{is}:$

1.  $\mathrm{V} = {\mathrm{V}}_{\mathrm{L}} - {\mathrm{V}}_{\mathrm{C}}$

2.  $\mathrm{V} = \sqrt{{\mathrm{V}}_{\mathrm{R}}^2 + {\mathrm{V}}_{\mathrm{L}}^2}$

3.  $\mathrm{V} = \sqrt{{\mathrm{V}}_{\mathrm{R}}^2 + {\left({\mathrm{V}}_{\mathrm{L}} - {\mathrm{V}}_{\mathrm{C}}\right)}^2}$

4.  Zero

When the speed of a dc motor increases the armature current 

(1) Increases

(2) Decreases

(3) Does not change

(4) Increases and decreases continuously

An electric motor operating on a 60 V dc supply draws a current of 10 A. If the efficiency of the motor is 50%, the resistance of its winding is 

(1) 3Ω

(2) 6Ω

(3) 15Ω

(4) 30Ω

The potential difference V and the current i flowing through an instrument in an ac circuit of frequency f are given by $V=5\cos \omega t$ 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

In an ac circuit, V and I are given by V = 100 sin (100 t) volts, $I=100\sin \left(100t+\frac{{\displaystyle \pi }}{{\displaystyle 3}}\right)mA$. The power dissipated in circuit is 

(1) 10⁴ watt

(2) 10 watt

(3) 2.5 watt

(4) 5 watt

The impedance of a coil, when DC supply is replaced by AC supply:
1. will remain the same
2. will increase
3. will decrease
4. will be zero

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

The peak value of an alternating e.m.f. E is given by $E=E_0\cos \omega t$ 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. $5\sqrt{3}V$

3. 5 V

4. 1 V