Tag: electric fuse

Questions Related to electric 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?

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

  1. A

  2. B

  3. A and B

  4. None of these

Show answer
Correct Option: B
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.

Which one of the following statements is not correct?

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

  1. The two main organs of the human body where the magnetic field produced is quite significant are the heart and the brain.

  2. In a house circuit, lamps are used in parallel

  3. Switches,fuses and circuit breakers should be placed in the neutral wire

  4. A generator with commutator produces direct current

Show answer
Correct Option: C
Explanation:

Switches, fuses and circuit breakers must be placed in the live wire, not in neutral wire. And all the other statements given are correct.

The commonly used safety fuse wire is made of

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

  1. copper

  2. lead

  3. nickel

  4. an alloy of tin and lead

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Correct Option: D
Explanation:

The commonly used fuse wire is made of an alloy of tin and lead.


Answer-(D)

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

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

  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.

Show answer
Correct Option: A,C
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.

The lighting circuit of the house has _______ fuse.

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

  1. 15A

  2. 50A

  3. 5A

  4. 500A

Show answer
Correct Option: C
Explanation:

Usually, there are two separate circuits in a house, the lighting circuit with a 5A fuse and the house circuit with a 15A fuse.

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

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

  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.

Show answer
Correct Option: A
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.

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

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

  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.

Show answer
Correct Option: B
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.

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

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

  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

Show answer
Correct Option: A
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. 

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

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

  1. melts

  2. cold

  3. proivides light

  4. hot

Show answer
Correct Option: A
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.

When a fuse is rated 8A, it means :

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

  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

Show answer
Correct Option: D
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.