Physics

Electrical Machines and Circuits

720 Questions

Electrical machines and circuits involve the principles of alternating and direct current, transformers, diodes, and power consumption. These concepts are essential for engineering and technical exams. Review these practice questions to test your knowledge of circuit analysis.

Transformers and impedanceAlternating and direct currentCircuit components and diodesPower consumption calculations

Electrical Machines and Circuits Questions

Multiple choice

Assume that the switch S is in position 1 for a long time and thrown to position 2 at t = 0.

At t = 0+, the current i1 is
  1. $\dfrac{-V}{2R}$
  2. $\dfrac{-V}{R}$
  3. $\dfrac{-V}{4R}$

  4. zero
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When the switch is in position 1 for a long time, the inductor reaches steady state with current I = V/R flowing through it (inductor acts as short circuit in DC steady state). At t=0+, the inductor current cannot change instantaneously, so it remains V/R. In position 2, this current flows through 2R, creating a voltage of -V/2R across the inductor to oppose the change.

Multiple choice

The effect of current shunt feedback in an amplifier is to

  1. increase the input resistance and decrease the output resistance

  2. increase both input and output resistances

  3. decrease both input and output resistances

  4. decrease the input resistance and increase the output resistance
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The given solution is right.                    Here  Ri  = input resistance without feedback                              Rif  = input resistance with feedback                              R of  = output resistance with feedback                  

Multiple choice

The Zener diode in the regulator circuit shown in figure has a Zener voltage of 5.8 Volts and a Zener knee current of 0.5 mA. The maximum load current drawn from this circuit ensuring proper functioning over the input voltage range between 20 and 30 Volts, is

  1. 23.7 mA

  2. 14.2 mA

  3. 13.7 mA

  4. 24.2 mA
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\text{The maximum load current will be at maximum input voltage i.e} \\ V_{max} = 30 V i.e \\ or \hspace{1cm} \frac{30 - 5.8}{1K} = I_L = 0.5 m \\ or \hspace{1cm} I_L = 24.2 - 0.5 = 23.7 mA$