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 electric current and its effects electric fuse electrical fuse and mcb fuse

You are given two fuse wires A and B with current rating 2.5 A and 6 A respectively. Which of the two wires would you select for use with a 1100 W, 220 V room heater?

  1. A

  2. B

  3. A and B

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Fuse is a piece of wire of a material with a very low melting point. When a high current flows through the circuit due to overloading or short circuit, the wires gets heated and melts. As a result, the circuit is broken and current stops flowing. 
The fuse must always be connected to the mains and it must be of correct value. For example, a 15-ampere fuse should trip when the current through it exceeds 15 amperes. A 20-ampere fuse should blow when the current through it exceeds 20 amps.
In this case, the electrical appliance is of 1100 W power and 220 V. So the current that passes through the appliance is calculated from P=VI. That is, I=P/V.
So, I = 1100 W/220 V = 5 A.
Hence, the wire B with current rating of 6 A should be used for the fuse.

Multiple choice physics electric current and its effects electric fuse electrical fuse and mcb fuse

Two identical fuses are rated at 10A. If they are joined

  1. in parallel, the combination acts as a fuse of rating 20A

  2. in parallel, the combination acts as a fuse of rating 5A

  3. in series, the combination acts as a fuse of rating 10A.

  4. in series, the combination acts as a fuse of rating 20A.
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

A fuse is a piece of wire resistance which acts in a way such that if the voltage in a circuit exceeds the rating of the fuse then the fuse wire melts and the circuit becomes an open circuit, thereby breaking the circuit and preventing the components from getting damaged due to short circuit. Now, if two fuses are in series, the melting of a single fuse can break the circuit and so in series the rating will be 10A. However, in parallel, even if one fuse is melted, the other fuse still works and so the net rating will be 20A.

Multiple choice physics electric current and its effects electric fuse electrical fuse and mcb fuse

What is the problem when a multi-plugs adaptor is used to connect many appliances to the same socket?

  1. The current drawn from the mains gets higher and overheating may occur.

  2. The voltage across the live and neutral wires increases and overheating may occur.

  3. The flow of the current will be slowed down and the power to each appliance will be reduced.

  4. The appliances will be damaged due to the higher current that flows through each appliance.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  • This means much amount of current will be drawn from the socket.
  • If we plug in a washing machine,a hair dryer ,a 1 HP mixer grinder then out socket will simply melt.
  • So by using multi-plugs adapter current drawn increase result in over heating.
Multiple choice physics electric current and its effects electric fuse electrical fuse and mcb fuse

What is the reason for the fuse and switch to be located at the live wire?

  1. To cut off the current from the appliance.

  2. To cut off the high voltage from the appliance.

  3. To break the circuit when there is a sudden current surge.

  4. To indicate to the user that the wire is Live wire when fuse and switch is seen on it.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When by short-circuit or any other reason current exceed its nominal value that time fuse breaks the circuit and so cuts off the high voltage from the appliance which prevent it from damage.

Multiple choice physics electric current and its effects electric fuse electrical fuse and mcb fuse

Choose the wrong option regarding miniature circuit breaker (MCB)?

  1. MCB contains a metal which melts when the current passing through it exceeds a certain value and hence opens the circuit

  2. Quick restoration of an MCB is possible just by switching on the operation when a breakdown occurs due to current overload

  3. MCB switchess off the circuit automatically when the current passing through it exceeds a certain value

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In MCB, whenever continuous current flows, the bimetallic strips is heated and deflect by bending. This deflection of bimetallic strips releases the mechanical latch. It causes to open the miniature circuit breakers contact and the MCB turns of thereby stopping he current to flow in the circuit. Hence $A$ is the wrong statement. 

Multiple choice physics electric current and its effects electric fuse electrical fuse and mcb fuse

If the current in a circuit rises too high, the fuse wire will ?

  1. melts

  2. cold

  3. proivides light

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

Fuse wire have high value of resistance so when high magnitude of current flows through it then due to melting point of it it melts by excessive heating. Fuse is used to protect the circuit from any accidental heavy flow of current.

Multiple choice physics electric current and its effects electric fuse electrical fuse and mcb fuse

When a fuse is rated 8A, it means :

  1. It will not work if current is less than 8A

  2. It has a resistance of 8 ohm

  3. It will work only if current is 8A

  4. It will burn if current exceeds 8A
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The work of fuse wire to protect electric appliances if some particular amount of current that should not be passed through is passed accidentally.


The resistance of fuse wire is set as such if current exceeds from a particular amount heat is produced and and temperature of the fuse wire increases and it reaches to it's melting point and it melts and circuit becomes an open circuit. 

So if a wire is rated 8 A, it means the resistance is set to such a value that if current is exceeded from 8 A value then fuse wire will melt down.

Multiple choice physics electric current and its effects electric fuse electrical fuse and mcb fuse

A fuse is used in an electrical appliance :

  1. To earth the appliance

  2. To protect the appliance and its cable

  3. To change the efficiency of the applicance

  4. To change the current rating of the applicance
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Fuse is a device used to save the electric current from overheating due to the sudden increase in the current in the circuit.
It protects the device and the user when the electric current is higher than the normal needed by a circuit, it blows up breaking the circuit.
Hence protecting the circuit from an a power overload.

Multiple choice physics electric current and its effects electric fuse electrical fuse and mcb fuse

Which of the following is false about fuse ?

  1. A fuse controls the current that flows to the appliance.

  2. A fuse increases the resistance in the circuit to minimize the current flow.

  3. A fuse allows high current to flow through the circuit without damaging the appliance.

  4. A fuse protects the wiring and the appliance in the circuit from overheating.
Reveal answer Fill a bubble to check yourself
B,C,D Correct answer
Explanation

A fuse is a type of low resistance resistor that acts as a sacrificial device to provide over current protection, of either the load or source circuit. It just controls the amount of current flowing.
It neither increase the resistance of the circuit nor it allows high current. It doesn't allow high current to pass but that doesn't mean, it protect appliances from heating.

Multiple choice physics electric current and its effects electric fuse electrical fuse and mcb fuse

Fuse blows because ........................... .

  1. There is a high voltage connected across the circuit

  2. There is a high current flowing through the circuit

  3. There is a high charge that has passed through the circuit

  4. The effective resistance of the circuit is too high
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Fuse are used to protect electric appliances at home from large magnitude of current. they are made up of very high resistance. fuse  blows up (Melts) due to overheating when the current through it exceeds the rated current.

Multiple choice physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

In any electric circuit, when the switch is on and the current is flowing through it why do the wire, switches, bulb or devices in the circuit become hot?

  1. Because of the heating effect of electric current

  2. Because of the magnetic effect of electric current

  3. Because of the luminous effect of electric current

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is because some of the electric energy is converted into heat energy, i.e., heating effect of electric current.

Multiple choice physics electric current and its effects thermal effect of electric current heating effect of electric current effect of electric current

A lamp is marked 60 W, 220 V. If it operates at 200 V, the rate of consumption of energy will _____

  1. decrease

  2. increase

  3. remain unchanged

  4. first increase then decrease
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Given power of bulb =60W
Voltage=220V
Power $=\dfrac{V^2}{R}$
$60=\dfrac{220\times220}{R}$
$R=(\dfrac{220\times220}{60})\Omega$
$R=(\dfrac{220\times22}{6})\Omega$         (1)
When voltage = 200V, resistance will be same
$P=\dfrac{200\times200}{R}$
From 1,
$=\dfrac { 200\times 200\times 6 }{ 220\times 22 } $
$\dfrac { 200\times 20\times 6 }{ 22\times 22 } $
$=49.5J/S$

We see that  power gets decrease.
Power = rate of consumption of energy,
So rate of consumption of energy.