Tag: electric fuse

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

The cable of an electric fan becomes so worn that the live wire makes electrical contact with the metal case The case is earthed The plug to the fan contains a 5 A fuse There is a current of 4 A when the fan works normally What will happen in this case?

  1. The current will run to earth and the fuse will not be affected

  2. The metal case will become very hot

  3. The metal case will become live and dangerous

  4. The fuse will melt and switch off the circuit
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Answer is D.

When the live wire (high potential) is in contact with the earthed metal case (zero potential) and since there is a potential difference, current flows. As there is little to no resistance in the completed path, the current flow is very large (larger than 4 A melting the fuse). The fuse melts due to high current surge and switches off the circuit.

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

On Diwali Mr.Antriksh wants to light his house with a number of $10 W (220 V)$ bulbs in parallel. If the house circuit has a fuse of $5 A$ then what is the maximum number of such bulbs he can use if he is not using any other electrical appliance in the circuit.

  1. $10$
  2. $11$
  3. $100$
  4. $110$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Answer is D.

The power dissipated is given as P=VI.
In this case, the power of each the bulb is 10 W which uses 220 V supply.
So, the amount of current used is I=P/V = 10/220 = 0.045 A. 
The fuse has a power rating of 5 A. Hence, 5 A / 0.045 A = 111 such bulbs can be connected in parallel with security.
Hence, Mr. Antriksh can use 110 bulbs without any problem. 

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

The function of a fuse wire is independent of :

  1. its specific resistance

  2. its radius

  3. its length

  4. current flowing through it
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Answer is C.

A fuse consists of a metal strip or wire fuse element, of small cross-section compared to the circuit conductors, mounted between a pair of electrical terminals, and (usually) enclosed by a non-combustible housing. The fuse is arranged in series to carry all the current passing through the protected circuit. The resistance of the element generates heat due to the current flow. The size and construction of the element is (empirically) determined so that the heat produced for a normal current does not cause the element to attain a high temperature. If too high a current flows, the element rises to a higher temperature and either directly melts, or else melts a soldered joint within the fuse, opening the circuit and the current stops flowing through it.
Hence, the length of the fuse wire is does not matter.

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

The material used for a fuse wire should have 

  1. Low melting point

  2. High melting point

  3. High electrode potential

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

The material used for a fuse wire must have a low melting point so that it melts as soon as excessive current passes through it and thus it can prevent the appliance from damage.

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

A car headlamp of 48 W works on the car battery of 12 V. The correct fuse for the circuit is 

  1. 5A

  2. 2A

  3. 3A

  4. 15A
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer is A.

Fuses are safety devices that are to be built into our electrical system. If there were no fuses and we operated too many appliances on a single circuit, the cable carrying the power for that circuit would get extremely hot, short circuit, and possibly start a fire. To prevent electrical overloads, fuses are designed to trip or blow, stopping the flow of current to the overloaded cable.
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 car headlamp is 48 W and the voltage is 12 V.
That is, P = VI, I = P/V = 48/12 = 4 A.
Hence, the fuse of 5 A should be connected to the circuit.

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

The circuit breaker device which can be used in place of a fuse is called

  1. CBD

  2. MCB

  3. MCD

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

Answer is B.

Fuse boxes contain safety devices called fuses or circuit breakers - MCB (Miniature Circuit Breaker) which are designed to prevent an excess of electric current entering your house by only allowing a certain maximum current to flow in. When the electrical current is too large, an electromagnet attracts a spring loaded switch which breaks the circuit and cuts the power supply. The switch must be reset before any current can flow again.

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

In an electric circuit, a fuse is connected :

  1. in the live wire

  2. in the neutral wire

  3. in the earth wire

  4. Any of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer is A.

The live wire and neutral wire, coming from the electric pole, enter a box fitted just outside our house which has a main fuse F1. The fuse is connected in series with the live wire. This is done so because it is only the live wire which has a high potential of 220 volts unlike the neutral wire which carries zero potential.

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

What is immaterial for an electric fuse?

  1. Its length

  2. Its radius

  3. Its specific resistance

  4. Current flowing through it
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Its length is immaterial for an electric fuse fuse is used to avoid danger due to high current if high current is passed through the fuse it burns and disconnect the power supply the thickness of fuse determines how much current can be pass hence fuse of any length can be used but it's thickness should be proper

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

Fuses are connected in ________ to the live wire:

  1. parallel

  2. series

  3. either way

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

Answer is B.

The live wire and neutral wire, coming from the electric pole, enter a box fitted just outside our house which has a main fuse F1. The fuse is connected in series with the live wire. This is done so because it is only the live wire which has a high potential of 220 volts unlike the neutral wire which carries zero potential.

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

The essential requirements of a fuse wire are ___________.

  1. High resistance and high melting point

  2. High resistance and low melting point

  3. Low resistance and low melting point

  4. Low resistance and high melting point
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The fuse wire is made of zinc, copper, silver, aluminum, or alloys to provide stable and predictable characteristics. Fuse should be of low resistance and low melting point as per the requirement current rating for overcurrent protection.