Tag: household circuits

Questions Related to household circuits

A battery is charged at a potential of 15V for 8 hours when the current flowing is 10A. The battery on discharge supplies a current of 5A for 15 hours. The mean terminal voltage during discharges is 14 V. The "Watt hour" efficiency of the battery is :-

power transmission household electricity household circuits electricity and magnetism physics

  1. 80%

  2. 90%

  3. 87.5%

  4. 82.5%

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Correct Option: C
Explanation:

% Watt hour efficiency = $\frac{E _{out}} {E _{in}} \times 100$
= $\frac{\left ( 14 \right )\left ( 5 \right )\left ( 15 \right )} {\left ( 15 \right )\left ( 10 \right )\left ( 8 \right )} \times 100 = 87.5$%

Watt-hour meter measures

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  1. Electric Energy

  2. Current

  3. Voltage

  4. Power

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Correct Option: A

Power transmission is carried out at ........................ and  ..........................?

power transmission household electricity household circuits electricity and magnetism physics

  1. high voltage, high current

  2. low voltage, high current

  3. high voltage, low current

  4. low voltage, low current

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Correct Option: C
Explanation:

One of the key concerns in the transmission of electricity is the power loss in transmission lines, dissipated as heat due to the resistance of the conductors.
The power loss ${P} _{loss} = { I }^{ 2 }R={ (\dfrac { P }{ V } ) }^{ 2 }R(\because p=VI)$
Since $P $and $R $ are fixed conditions, less power will be lost if high voltages V are used.
The transmission line then uses a transformer to step down the voltage.
For a given amount of power, a higher voltage reduces the current and thus the resistive losses occurs in the conductor. For example, raising the voltage by a factor of 10 reduces the current by a corresponding factor of 10 and therefore the$ {I}^{2}{R}$ losses by a factor of 100, provided the same sized conductors are used in both cases. 

X bulbs each of 80 watts are used for 5 hours a day for 30 days and they consume an electrical energy of 60 kWh. Then X is

power transmission household electricity household circuits electricity and magnetism physics

  1. 1

  2. 3

  3. 5

  4. 7

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Correct Option: C

A town situated $20km$ away from a power house at $440V$, requires $600KW$ of electric power at $220V$. The resistance of transmission line carrying power is $0.4\Omega$ per km. The town gets power from the line through a $3000V-220V$ step down transformer at a substation in the town. Which of the following is /are correct

power transmission household electricity household circuits electricity and magnetism physics

  1. The loss in the form of heat is $640KW$

  2. The loss in the form of heat is $1240KW$

  3. Plant should supply $1340kW$

  4. Plant should supply $640kW$

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Correct Option: A
Explanation:

Total length of wire = $20 \times 2 = 40km$


Resistance of wire $R = 40 \times 0.4 = 16\Omega $ ,


${I _{\max }} = \dfrac{P}{V} = \dfrac{{600kW}}{{3000V}} = 200A$

Power loss in the form of heat $ = {I^2} _{rms} \times R = {\left( {200} \right)^2} \times 16 = 640kW$

Which one has not the same unit as other?

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  1. watt sec

  2. kilowatt hr

  3. e V

  4. J sec

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Correct Option: C

These questions consist of two statements each, printed as assertion and reason. While answering these questions you are required to choose anyone of the following four responses.


Assertion: Long distance power transmission is done at high voltage. 

Reason: At high voltage supply power losses are less. 

power transmission household electricity household circuits electricity and magnetism physics

  1. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

  2. If both Assertion and Reason are true but the Reason is not the correct explanation of the Assertion.

  3. If Assertion is true statement but Reason is false.

  4. If both Assertion and Reason are false statements.

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Correct Option: A
Explanation:

Long distance power transmission is done at high voltage.

Since power loss 
${ P } _{ loss } = { I }^{ 2 }R = { \left( \dfrac { P }{ V }  \right)  }^{ 2 }R$
Here P & R are fixed conditions so less power will be lost if high voltage V are used.
At high voltage supply power loss are less.
Both assertion and reason are correct and reason correctly explains assertion 
Option A is correct.

An electric meter measures the electrical energy consumed in :

power transmission household electricity household circuits electricity and magnetism physics

  1. Joules

  2. Calorie

  3. Kilowatt hours

  4. Ergs

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Correct Option: C
Explanation:

The electric meter used in home measures electric energy consumed in units of $kWh$ that is $kilowatt$ $hours$.


$1kWh=1kW\times 1h$

         $=1000W\times\times 3600s$

$\implies 1kWh=3.6\times 10^6 J$

Answer-(C)

Which is not a correct advantage of parallel combination in domestic circuit?

power transmission household electricity household circuits electricity and magnetism physics

  1. Same voltage of the mains is available for all electrical appliances

  2. Switching on or off one switch has no effect on the other

  3. If one appliance stops working, other appliances keep in working

  4. none

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Correct Option: D

Power is transmitted from a power house on high voltage ac because :

power transmission household electricity household circuits electricity and magnetism physics

  1. The rate of transmission is faster at high voltage

  2. It is more economical due to less power wastage

  3. The life of the current carrying wire is prolonged

  4. A precaution-against the theft of transmission line

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Correct Option: B
Explanation:

The higher the voltage V, the lower the current I and therefore much lower power loss.Transmitting electricity at high voltage reduces the fraction of energy lost to resistance