Tag: physics

Questions Related to physics

An electric bulb rated 220 V - 100 W will fuse if it consumes 131 W. What voltage fluctuations can it withstand?

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

  1. up to 230 V

  2. up to 241 V

  3. up to 225 V

  4. up to 252 V

Show answer
Correct Option: D
Explanation:

We know that: $P = \dfrac{V^{2}}{R}$
Using the fact that the bulb is $220V - 100W$
$ 100 = \dfrac{220^{2}}{R}$

$R = \dfrac{48400}{100} = 484\ ohm$

Given that it will fuse on use of power of $131W$.
Substituting this:
$131 = \dfrac{V^{2}}{484}$

$V^{2} = 131 \times 484 = 63,404$

$\Rightarrow V = 251.8V$   Which is the highest voltage it can experience without fusing.

An 1800 W toaster, a 1.3 kW frying pan are plugged into the same $20 A-120V$ line then

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

  1. fuse will not blow

  2. fuse will blow

  3. supply will spark

  4. fuse is just saved

Show answer
Correct Option: B
Explanation:

$I _{toaster}=\dfrac{1800}{120}= 15 A,$


$I _{frying pan}=\dfrac{1300}{120}= 10.83 A$

$I _{net}= 25.83 A > 20 A$ 

because applied current is more than possible value of current which is given in ques. Hence fuse will blow

A fuse wire of radius $0.2$ mm blows out for a current of $5A$. For what current, another fuse wire of same material but of radius $0.3$ mm will blow out?

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

  1. $5$A

  2. $3.2$A

  3. $4.33$A

  4. $11.2$A

Show answer
Correct Option: A

A fuse wire of circular cross-section and having diameter of $0.4$ mm, allows $3$A of current to pass through it. But if another fuse wire of same material and circular cross-section and having diameter of $0.6$ mm is taken, then the amount of current passed through the fuse is?

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

  1. $3$A

  2. $3\times \sqrt{\dfrac{3}{2}}$A

  3. $3\times\left(\dfrac{3}{2}\right)^{3/2}$A

  4. $3\times \left(\dfrac{3}{2}\right)$A

Show answer
Correct Option: C

what is a fuse ?

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

  1. Over current protection

  2. low resistance and high melting point wire.

  3. low resistance and low melting point wire.

  4. high resistance and low melting point wire.

Show answer
Correct Option: A,D
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 fuse element is made of zinc, copper, silver, aluminum, or alloys to provide stable and predictable characteristics.
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.

What we used to protect the electric circuits from over loading and short circuit ?

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

  1. capacitance

  2. inductance

  3. fuse wire

  4. filament wire.

Show answer
Correct Option: C
Explanation:

A  fuse is the device to protect the electric circuits from over loading and short circuit.
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 fuse element is made of zinc, copper, silver, aluminum, or alloys to provide stable and predictable characteristics.
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. Hence correct option is C.

Complete the following sentences : 

A fuse is a short piece of wire of high .......... and of material of low ..........

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

  1. resistance, melting point

  2. meting point, resistance

  3. capacitance, melting point.

  4. conductance, melting point

Show answer
Correct Option: A
Explanation:

A  fuse is the device to protect the electric circuits from over loading and short circuit.
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 fuse element is made of zinc, copper, silver, aluminum, or alloys to provide stable and predictable characteristics.
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.
Hence, A fuse is a short piece of wire of high resistance and of material of low melting point.

Complete the following sentences :

A fuse wire is made of an alloy of .......... and ..........

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

  1. lead, tin

  2. nickel , lead

  3. cadmium, lead

  4. nickel, tin

Show answer
Correct Option: A
Explanation:

A  fuse is the device to protect the electric circuits from over loading and short circuit.
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 fuse element is made of zinc, copper, silver, aluminum, or alloys to provide stable and predictable characteristics.
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.
Hence, A fuse wire is made of an alloy of lead and tin If the current in a circuit rises too high, the fuse wire melts.

Hence correct option is option A.

The rating of a fuse connected in the general household lighting circuit is:

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

  1. 15 A

  2. 5 A

  3. 10 A

  4. zero

Show answer
Correct Option: B
Explanation:

General household wire has a current supply of 5 ampere. Hence fuse also have that. hence The rating of a fuse connected in the general household lighting circuit is $5A$

 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 ? 

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

  1. 25 A, yes

  2. 2.5 A, yes

  3. 25 A, no

  4. 2.5 A, no

Show answer
Correct Option: C
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.