A 106 mF capacitor is connected in series with a 40 W resistor across a 250 V, 50 Hz supply. Calculate: (a) the impedance, (b) the current, (c) the power factor (state whether lag or lead).

Calculate, for the circuit shown in the opposite figure, (a) the circuit current, (b) the voltage across the capacitor, (c) the supply voltage, and (d) the phase angle of the circuit.

A coil, of resistance 8 W and inductance 0.0128 H, is connected to a 150 V, 50 Hz supply. Calculate: (a) the impedance of the coil, (b) the current which will flow, (c) the power factor, (d) the power absorbed by the coil.

When a c. supply at 240 V is applied to the ends of a certain choking coil, the current in the coil is 20 A. If an a.c. supply at 240 V, 50 Hz, is applied to the coil, the current in the coil is 12.15 A. Calculate the resistance, impedance, inductance, and reactance of the coil.

5) A circuit comprises a resistance of 6 W, an inductance of 0.05 H and a capacitance of 320 mF, all connected in series. An alternating supply at 240 V, 50 Hz, is applied to the ends of the circuit. Calculate the current taken.

6) A coil having a resistance of 5 W and an inductance 0f 0.2 H is connected in series with a capacitor of 150 mF to 100 V, 50 Hz mains. Find: (a) the voltage across the coil and (b) the power factor of the whole circuit stating whether it is lagging or leading.

7) A single-phase a.c. circuit consists of a non-inductive resistance coil of 20 W, an inductive coil of negligible resistance, and a capacitor all connected in series across a 50 Hz supply. The voltage applied across each component in turn gave the following readings:

across resistance coil 192 V

across capacitor 56 V

across inductive coil 200 V

Calculate: (a) the inductance, (b) the capacitance, (c) the power factor.

8) A circuit consists of a non-inductive resistor of 10 W, an inductor of 0.1 H, and a capacitor of 8 mF in series. Find: (a) the current, (b) the resonant frequency, (c) the voltage across each component when an e.m.f. of 25 V at resonant frequency is applied to the whole circuit.

9) Calculate the value of the capacitor required to give resonance at 50 Hz when in series with a coil of resistance 4 W and inductance 0.2 H. What voltage magnification is obtained?

10) The input power to a 400 V, 50 Hz supply circuit is 6 kW. If the load current is 20 A at a lagging power factor calculate: (a) the power factor, (b) the apparent and reactive power, (c) the resistance, reactance, impedance, and inductance of the circuit.

11) A single-phase load comprises three parts: (a) 10 kVA at a power factor of 0.8 lagging, (b) 20 kVA at a power of 0.6 lagging, (c) 15 kVA at a power factor of 0.7 leading. Find: (i) the total kW, (ii) the total kVAr, (iii) the power factor of the total load.

The load taken from an a.c. supply consists of (a) a heating load of 15 kW, (b) a motor load of 40 kVA at 0.6 power factor lagging, (c) a load of 20 kW at 0.8 power factor lagging. Calculate the total load from the supply in kW and in kVA and its power factor. What would be the kVAr rating of a capacitor to bring the power factor to unity, and how would the capacitor be connected?

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Posted on May 6, 2016Author TutorCategories Question, Questions