Physics

Electrical Machines and Circuits

754 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 physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

Alternating current can not be measured by $D.C$. ammeter because 

  1. $A.C$. cannot pass through $D.C$.
  2. $A.C$. changes direction

  3. average value of current for complete cycle is zero
  4. $D.C$. ammeter will get damaged.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

While for half-circle, the value of current is different at different points and for complete cycle its average value is zero.

So, we can't measure current by $D.C$ ammeter .

Multiple choice physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

Which of the following can be true?

  1. The instantaneous power output of an ac source can be negative.

  2. The average power output of an ac source can be negative.

  3. The instantaneous power output of an ac source can NOT be negative.

  4. The average power output of an ac source can NOT be negative.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In an AC circuit, the instantaneous power p = v*i can be negative if the voltage and current have opposite signs, which occurs when the phase difference is between 90 and 270 degrees.

Multiple choice physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

Marking on a bulb is 60 W, 220 V. What does it signify ?

  1. The bulb is connected across 220 volts, 60 joules of energy is released in every second.

  2. The bulb is connected across 220 volts, 60 joules of energy is released in every minute.

  3. 60 A of current will flow in the bulb.

  4. 220 A of current will flow in the bulb.
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

Fill the blank.
Voltmeter is always connected in . . . .with the device.

  1. series

  2. parallel

  3. series and parallel both.

  4. the cell.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit. A voltmeter is connected in parallel with a device to measure its voltage.
Hence, the statement is false as the voltmeter is connected in parallel to the device in a circuit.

Multiple choice physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

A certain network consists of two ideal and indentical voltage sources in series and a large number of ideal resistor. The power consumed in one of the resistor is $4W$ when either of the two sources is active and other is replaced by a short circuit. The power consumed by same resistor when both sources are simultaneously active would be: 

  1. $0$ or $16W$
  2. $4W$ or $8W$
  3. $0$ or $8W$
  4. $8W$ or $16W$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$ P=VI$

$ I= \cfrac{nE}{R+r}$ (r=0)
In this case 
$ I= \cfrac{nE}{NR} ; E _1 = E _2$
$ P=VI$
In first case 
$ 4 =E \times \cfrac{E}{NR} = \cfrac{E^2}{NR}$
In second case 
$ x =2E \times \cfrac{2E}{NR} = \cfrac{4E^2}{NR}$
$ \cfrac{x}{4} = \cfrac{4E^2}{NR} \times \cfrac{NR}{E^2}$
$ x= 0 \quad or \quad 16W$

Multiple choice physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

The maximum current which can flow through a fuse without melting it is called its

  1. potential

  2. power

  3. rating

  4. capacity
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The maximum current which can flow through a fuse without melting it is called its rating.
For example a fuse rated at 8 A, can stand current upto 8 A. If current higher than 8 A flows through the fuse, it would melt and circuit gets broken.the rating of a fuse depends upon the thickness of the fuse wire (because length of the wire is fixed). The thicker fuse has higher rating. So, the thickness of the fuse wire in 8 A circuit is more than that of the fuse wire in 5 A circuit.

Multiple choice physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

All appliances in a domestic electric circuit are connected in parallel so that

  1. Voltage drop across each appliance is same.

  2. Current through each appliance is same.

  3. Power consumed by each appliance is same.

  4. It allows amplification of power
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Voltage drop is the driving force in any electrical circuit. Hence, it is desired to supply same voltage everywhere.

Multiple choice physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

Potential difference of 220-250 V is present between 

  1. Earth wire and neutral wire

  2. Live wire and earth wire

  3. Live wire and neutral wire

  4. B and C both
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Potential difference between live wire and neutral wire is about 220 V-250 V. which is generally provided for household purposes in homes for electricity. so correct option is C.

Multiple choice physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

The rating of a fuse depends upon the

  1. thickness of the fuse wire

  2. length of the wire

  3. both

  4. none
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The maximum current which can flow through a fuse without melting it is called its rating.
For example a fuse rated at 8 A, can stand current upto 8 A. If current higher than 8 A flows through the fuse, it would melt and circuit gets broken.

The rating of a fuse depends upon the thickness of the fuse wire(because length of the wire is fixed).the thicker fuse has higher rating. So, the thickness of the fuse wire in 8 A circuit is more than that of the fuse wire in 5 A circuit.

Multiple choice physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

For a domestic $AC$ supply of $220\ V$ at $50$ cycles per second the potential difference between the terminals of a two-pin electric outlet in a room is given by

  1. $V(t) = 220\sqrt {2}\cos (100\pi t)$
  2. $V(t) = 220\cos (50t)$
  3. $V(t) = 220\cos (100\pi t)$
  4. $V(t) = 220\sqrt {2}\cos (50 t)$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Rms value of voltage  $V _{rms} =220 $ volts

Peak value of voltage  $V _o = \sqrt{2}V _{rms}$
$\therefore$ $V _{o} = 220\sqrt{2}$volts   
Frequency  $\nu =50$ $Hz$
$\implies$  $w = 2\pi \nu = 2\pi (50)  = 100\pi$
Thus potential difference is given by  $V = V _o \cos wt$
$\therefore$  $V= 220\sqrt{2} \cos (100 \pi t)$