DieselShip's Online Content Library

Q4. A non-linear resistor whose characteristic is given by I = KV^1/2 is connected in series with a variable resistance across a 120 V d.c. supply. When the variable resistance is set to 56  the current in the circuit is 1A. Calculate EACH of the following:

(a) the value of the constant K;

(b) the value to which the variable resistance must be set to make the current 0.75 A;

(c) the power dissipated in the non-linear resistor when the current is 0.75 A.

Q5. A simple voltage stabilizer circuit consists of a 1 Watt Zener diode and a series resistance R. The Zener diode has a breakdown voltage of 12 V and a slope resistance of 2W. It requires a minimum current of 2 mA for successful stabilization. The unregulated d.c. input voltage can vary between 18 V and 24 V. Calculate EACH of the following:

(a) The minimum value of the resistor R if the output current is zero and the input voltage is a maximum of 24 V;

(b) The maximum output current which can be drawn when the input voltage is 18 V if satisfactory stabilization is to be maintained;

(c) The power dissipated in the Zener diode in Q3 (b).

Q7. A single phase a.c. circuit comprises a coil of inductance 0.5 H and resistance 100 Ω in series with a capacitor ‘C’. It is connected to 120 V, 50 Hz and draws a current at a leading power factor. The volt drop across the coil is 150 V. Calculate EACH of the following:

(a) The current in the circuit;

(b) The value of the capacitor;

(c) The power factor of the circuit;

(d) The power dissipated in the circuit.

Q7. A balanced star connected three phase load has a coil of inductance 0.2 H and resistance 50 W in each phase. It is supplied at 415 V, 50 Hz. Calculate EACH of the following:

(a) The line current;

(b) The power factor;

(c) The value of each of three identical delta connected capacitors to be connected across the same supply to raise the power factor to 0.9 lag;

(d) The new value of the line current.