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Q16. For the network shown in Fig Q1, Calculate EACH of the following:

(a) The currents I₁, I₂ and I₃;

(b) The p.d. across the 100Ω resistor;

(c) The power dissipated in the 8Ω resistor.

Q9. A coil of inductance 2 H and unknown resistance is connected to a D.C. supply of 100 volts. After 4 ms the current has risen to 75% of its final steady state value. Calculate EACH of the following:

(a) The resistance by the coil;

(b) The energy stored in the coil when the current has reached its steady state value;

(c) The time taken for the current to fall to 50% of its steady state value when the supply Is switched off.

Q9. The p.d. across the base-emitter junction of the silicon transistor shown in Fig Q3 is 0.6 V and the steady state voltage at the collector is 4 V.

Calculate EACH of the following, assuming the base current is negligible:

(a) The p.d across each of the bias resistors;

(b) The p.d between the collector and emitter of the transistor;

(c) The value of the load resistor RL;

(d) The power dissipated in RL;

(e) The power dissipated in the transistor.

Q9. A single-phase circuit comprises a coil having resistance and inductance, 45Ω resistor and a capacitor in series across a 40 V variable frequency supply. When the frequency is 400 Hz, the current reaches its maximum value of 0.8 A and the voltage across the capacitor is 170 V.

(a) Calculate EACH of the following:

(i) The value of the capacitor;

(ii) The resistance and inductance of the coil;

(iii) The p.d. across the coil;

(iv) The supply kVAR.

(b) Sketch a phasor diagram showing ALL the volt drops in relation to the circuit current.

Q11. Three identical coils are delta connected to a 3 ph, 440 V, 60 Hz supply and consume a total power of 9 kW at a power factor of 0.8 lag.

(a) Calculate the resistance and inductance of EACH coil.

(b) If the same three coils are now connected in star to the same supply, calculate the current in each line if:

(i) One coil is short circuited;

(ii) One coil is open circuited

Q4. A three phase, six pole, delta connected induction motor is supplied at 380 V, 60 Hz. It draws a current of 45 A at a power factor of 0.85 lag. The stator losses are 4 kW and the windage and friction losses total 3 kW. It runs at 19 rev/s. Calculate EACH of the following:

(a) The rotor copper loss;

(b) The shaft output power;

(c) The shaft output torque.