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Q14. (a) For the measuring network shown in Fig Q1 calculate the resistance (RM) of the moving coil instrument if it is to read 10 mA.

(b) Calculate the reading on the instrument if the 100 Ω and the 80 Ω resistors are interchanged.

Q2. A non-linear element is connected in series with a resistor across 240 V d.c. supply.

The non-linear element is governed by the la I = kv². When the resistor is set to 10W the supply current is 12 A.

(a) Calculate EACH of the following:

(i) The resistance value required to reduce the current to 8 A:

(ii) The resistance of the nonlinear element when the current is 8A.

(b) The supply voltage is reduced to 159 V. calculate the power dissipated in the non-linear element if the series resistor is reset to 10W.

Q6. A simple voltage stabilizer consists of a 1 W Zener diode and a series resistor ‘R’ as shown in Fig. The Zener diode has a breakdown voltage of 12 V and a slope resistance of 2 It requires a minimum current of 2 mA for successful stabilization. The unregulated input voltage can vary between 18 V and 24 V. Calculate EACH of the following:

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

(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 by 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.

Q9. A three phase four wire unbalanced system has a current in the red phase of 10 A at unity power factor and the current in the yellow phase is 8 A lagging by 30°. If the current in the neutral is 3.07 A in phase with the red phase voltage, calculate EACH of the following:

(a) The magnitude of the current in the blue line;

(b) Its angular relationship to the blue line voltage;

(c) The total power dissipated in the three phase loads if the value of the phase voltage is 240 V.

Q3. A 6 pole, three phase squirrel cage induction motor runs on a 415 V, 60 Hz supply. It draws a line current of 85 A at a power factor of 0.75 lag. The shaft speed is 19 revs/sec. If the iron losses are 2 KW, the stator copper loss is 1 KW and the rotational losses (windage and friction) are 1.5 KW, calculate EACH of the following:

(a) The slip as a per unit value;

(b) The rotor copper loss;

(c) The shaft output power;

(d) The efficiency.