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 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

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  $V = V _o \cos wt$
$\therefore$  $V= 220\sqrt{2} \cos (100 \pi t)$

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

Household electrical appliances are joined using ________ combination of resistors

  1. Parallel

  2. Alternating

  3. Continuous

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

In a house, there are many electrical appliances that have to run independent of each other. If one appliance is turned on or off it should not affect the other appliances. Thus even if a single appliance is taken out of the circuit (turned off / open switched ) the circuit breaks and hence the current cannot flow in the circuit so every thing turns off.

 So even if a single appliance is taken out of the circuit (turned off / open switched ) the circuit breaks and hence the current cannot flow in the circuit .
In parallel, even if an appliance gets damaged or is turned off ,the current always has other independent dedicated parallel paths to other appliances and hence every appliance is still works well. 

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

Which statement is wrong from the following?

  1. The earthing wire is green coloured.
  2. In India, current flowing through wire is AC and its frequency is $50 \,Hz$.
  3. In India, voltage between two wires is $110 \,V$.
  4. T.V., Tublight, bulbs are connected with $5\, A$ line.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In India, current flowing through wire is A.C and its frequency is $50Hz$ and voltage $220V$.But, Option C said voltage between two wires is 110V110V, which is wrong.

Therefore, C is correct option.

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

Which of the following statements is true?

  1. In tree type distribution of electric power, fuses are present only on the main board.

  2. In ring type distribution of electric power, there is an individual fuse for each appliance.

  3. Ring type distribution of electric power is advantageous than the tree type distribution.

  4. All the above.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In tree type distribution of electric power, fuses are present only on the distribution board where as in ring type, there is an individual fuse for each appliance. As there is an individual fuse for each appliance in ring type, only faulty appliance will not work and all the other appliances will not be affected. It is easier to install. So, ring type is advantageous than that of tree type. Hence, choice is (4)