Tag: electric current and its effects

Quizzes (8) Questions (195)

Questions Related to electric current and its effects

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

 What is the current through an electrical appliance of rating 5 kW, 200 V and can you use a fuse which is rated 8 A ? 

  1. 25 A, yes

  2. 2.5 A, yes

  3. 25 A, no

  4. 2.5 A, no
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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, let us consider a device of power 5 kW, that is, 5000 W and 200 V.

The current through the appliance is given as $I=P/V.$

That is, $I=\dfrac { P }{ V } =\dfrac { 5000 }{ 200 } =25A$.

The fuse of 8 A cannot be used because the current through the appliance is 
greater the fuse rating. When the 25 A current flows through the fuse it will 
blow off and it will not be able to fulfill it purpose.

Hence, a fuse is rated 8 A cannot be used with this appliance.

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

Two fuse wires of same length are rated 5 A and 20 A. Which is the correct ?

  1. both wire will be same thickness.

  2. 20 A wire is more thicker

  3. 5 A wire more thicker

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

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.
As we know, the cross-sectional area of the wires will affect the amount of resistance. Wider wires have a greater cross-sectional area. Water will flow through a wider pipe at a higher rate than it will flow through a narrow pipe. This can be attributed to the lower amount of resistance that is present in the wider pipe. In the same manner, the wider the wire, the less resistance that there will be to the flow of electric charge. When all other variables are the same, charge will flow at higher rates that is, more current through wider wires with greater cross-sectional areas than through thinner wires.
Hence, the 20 A wire is the thicker wire as more amount of current flow through it than the 5 A wire.

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

Which are the correct for fuse wire?
 

  1. High resistance

  2. low resistance.

  3. low melting point.

  4. high melting point.
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

The electrical resistance of an electrical conductor is the opposition to the passage of an electric current through that conductor. The SI unit of electrical resistance is the ohm $\Omega $.
When the opposition to the passage of an electric current through that conductor is more it is called high resistance and when the opposition to the passage of an electric current through that conductor is less it is called low resistance.
The amount of resistance determines whether the circuit is a good conductor low resistance, or a bad conductor high resistance. 

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

Which one is correct for fuse wire ?

  1. low resistance and low melting point

  2. high resistance and high melting point

  3. high resistance and low melting point

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

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.
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. 
Hence, the statement is true as the material used for fuse has low melting point.

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

Which one of the following statements is not correct?

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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.