3. Electrical fundamentals - Q&A

A sine wave has 5 amps RMS value. What is the peak value?

• 7.07 amps.
• 6.37 amps.
• 10 amps.

An inductor has 1,000 turns of wire and a cross sectional area of 0.001m2. If the core has a permeability of 0.000,001 and the coil is 0.1m. What is the value of the inductor?

• 100microH.
• 100mH.
• 10mH.

An example of a paramagnetic material is

• silver.
• iron.
• glass.
• aluminium.

A Transformer has 4500 secondary turns and 750 primary turns. Its turns ratio is

• 1:6.
• 1:1.
• 6:1.

If the current reaches a maximum through an inductor of 2A in 15 seconds, what is the current after 3 seconds?

• 1.26A.
• 0.63A.
• 1A.

Two inductive coils are placed in close proximity with each other at 90 degrees. The number of flux linkages is

• 0.
• maximum negative.
• maximum positive.

A heater which consumes 800 Kilojoules/sec is on for 4hrs 15min. The energy consumed is

• 340 kWh.
• 4 kWh.
• 3400 kWh.

Transformer copper loss on full load is 220 Watts. On half load the loss will be

• 440 Watts.
• 110 Watts.
• 55 Watts.

An electric motor produces a force of 5 N at a distance of 0.2m from the centre of rotation and rotates at a speed of 100 revs/sec. The motors output is

• 100 horsepower.
• 628.4 watts.
• 314.2 watts.

In an inductive resistive circuit, 1 amp flows from a supply of 100V dissipating 50 Watts of power. The phase angle is

• 60degrees.
• 90degrees.
• 45degrees.

A transformer has 500 turns on the primary and 100 turns on the secondary. The secondary supplies 20V and is connected to a 10 ohm load. The primary current is

• 0.4 amps.
• 2 amps.
• 10 amps.

The RMS value of 200 volts peak to peak is

• 141.4 volts.
• 70.7 volts.
• 127.4 volts.

In a circuit containing three resistors of equal value connected in parallel, one resistor goes open circuit. The current in the other two resistors will

• decrease.
• increase.
• remain the same.

The total current flowing in a circuit of 200 lamps in parallel, each of a resistance of 400 ohm and connected across an input of 100 volts is

• 25 amps.
• 50 amps.
• 40 amps.

The time required to fully charge a 1 uF capacitor in series with a 100k ohm resistor is

• 100 seconds.
• 100 milliseconds.
• 500 milliseconds.

A sine wave of RMS value 7.07 volts has a peak to peak value of

• 20 volts.
• 10 volts.
• 0.707 volts.

Which of the following would be used to calculate a transformer's transformation ratio?

• Secondary turns / primary turns.
• Primary turns * secondary turns.
• Primary turns / secondary turns.

The SI unit of work is the

• Watt.
• Newton Meter.
• Joule.

What is the mutual inductance if two coils of 10mH and 500mH have 90% of the flux transferred from one to the other?

• 459mH.
• 5mH.
• 63mH.

A 20 Picofarad capacitor with a 1 Megohm resistor takes how long to charge?

• 100 microseconds.
• 20 milliseconds.
• 1 second.

In a an DC motor, the rotation of the MNA

• is opposite to the rotation of the armature.
• is slightly less speed than the rotation of the armature.
• is the same as the rotation of the armature.

Armature reaction in a DC generator causes

• MNA to move in the opposite direction of rotation.
• MNA to move in the direction of rotation.
• GNA to move in the direction of rotation.

What is the reflected impedance in the primary of the transformer circuit shown?

• 20 ohms
• 500 ohms
• 50 ohms

What happens to the current in a series resistive resonant circuit?

• It is maximum.
• It is minimum.
• It is zero.

Potentiometers are used as a

• variable voltage source.
• variable resistor.
• variable current source.