Basic Electrical Engineering

The RMS value of alternating current is the value of DC current that produces

1. Same magnetic field only
2. Same peak value
3. Same heating effect
4. Same frequency

In a DC motor, the function of commutator is to

1. Reduce losses
2. Convert AC armature current into unidirectional torque-producing current
3. Increase field flux
4. Act as load

The power factor of a purely resistive circuit is

1. 0
2. 5 lagging
3. 1
4. 8 leading

A commonly used solder in electrical work is an alloy of

1. Copper and zinc
2. Tin and lead
3. Iron and carbon
4. Aluminium and nickel

In a three phase star connection, the line voltage is

1. Equal to phase voltage
2. Less than phase voltage
3. √3 times phase voltage
4. 3 times phase voltage

A star-connected network has arms 3 Ω, 3 Ω and 3 Ω. The equivalent delta resistance of each side is

1. 3 Ω
2. 6 Ω
3. 9 Ω
4. 12 Ω

A 12 V DC source feeds two series resistors of 2 Ω and 4 Ω. The voltage across the 4 Ω resistor is

1. 4 V
2. 6 V
3. 8 V
4. 12 V

Eddy current loss can be reduced by

1. Using solid thick core
2. Laminating the core
3. Increasing current
4. Reducing number of turns to zero

A balanced three-phase load takes line voltage 400 V and line current 10 A at 0.8 pf. Total power is

1. 3200 W
2. 4000 W
3. 5542 W
4. 6928 W

Magnetomotive force is analogous to

1. Electric current
2. Resistance
3. Voltage
4. Conductance

An unknown impedance of Z Ω is connected in series with (5 + j8) Ω. If the current in the circuit is I = 2.5∠−15^\circ A, find the value of Z.

Draw a neat sketch of a D.C. generator. State the functions of each part and derive the e.m.f. equation.

What are eddy currents? Explain the cause of eddy current loss and the methods used to reduce it in transformers.

Explain the soldering process in detail.

Apply Thevenin's theorem to calculate the current through the 5 Ω resistor.

Derive the expression for energy stored in a magnetic field.

Explain the operating principle of a three-phase induction motor. How is a rotating magnetic field produced?

Find the equivalent resistance between terminals A-B in the resistance network

A three-phase load consists of three similar inductive coils, each of resistance 50 Ω and inductance 0.3 H. The supply is 415 V, 50 Hz. Calculate: (a) the line current; (b) the power factor; and (c) the total power when the load is star-connected.

Draw and explain the wiring layout of a small residential installation consisting of lamps, a fan, a socket outlet, a switchboard, a main switch, an energy meter, and a distribution board.

Derive the torque equation of a D.C. motor.

Obtain a single current source for the network shown below

An 8-pole lap-connected armature has 40 slots with 12 conductors per slot and generates a voltage of 500 V. Determine the speed at which it is running if the flux per pole is 50 mWb.

Explain the principle of operation and construction of a single-phase transformer.

Maximum Power Transfer Theorem

Classify DC machines

State and prove Norton's theorem

Average and RMS value of a sinusoidal voltage