Tag: physics

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Multiple choice power transmission household electricity household circuits electricity and magnetism physics

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. 

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

Multiple choice power transmission household electricity household circuits electricity and magnetism physics

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

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

All options A, B, and C are correct advantages of a parallel circuit in a domestic setting. Since the question asks for a 'not correct' advantage and none of the listed options are incorrect, 'none' is the correct choice.

Multiple choice power transmission household electricity household circuits electricity and magnetism physics

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

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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

Multiple choice power transmission household electricity household circuits electricity and magnetism physics

Transmission lines transmit a voltage of $V$ volt to our houses from power stations, then the power $P$ supplied by them is proportional to:

  1. $\cfrac{1}{V}$

  2. $V$

  3. ${V}^{2}$

  4. $\cfrac{1}{{V}^{2}}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Power supplied is equal to to the voltage multiplied by the current flowing through the wire.

  $\therefore$     $P = VI$
$\implies  P  \propto  V$

Multiple choice power transmission household electricity household circuits electricity and magnetism physics

From a power station, the power is transmitted at a very high voltage because :

  1. It is generated only at high voltage

  2. It is cheaper to produce electricity at high voltage

  3. Electricity at high volatge is less dangerous

  4. There is less loss of energy in transmission at high voltage
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When power is transmitted from power station to different different substation then one important factor is kept in mind that power loss in pathway during transmission over large distances should be minimum. 

we know that P = V I 
so for a particular power that is to be transmitted we can choose a combination of voltage and current so that loss is minimum as much possible.
if we do current high and voltage minimum then due to high current , heat loss will be more and power will get lost , hence voltage is kept high and current is kept low as much possible so that current can not produce high vibrations and collisions  in free electrons insides the wire making a lot of loss of power.
so by keeping voltage to high value the loss is minimum as compared to other cases.

Multiple choice power transmission household electricity household circuits electricity and magnetism physics

A boy of mass $55\ kg$, runs up a flight of $40$ stairs, its measuring $0.15\ m$ in $15\ s$, the power developed by the boy in kilowatts and Horse power is

  1. $220$ and $0.29$

  2. $625$ and $0.83$

  3. $1.15$ and $0.83$

  4. $6.25$ and $0.83$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Work = m * g * h = 55 * 9.8 * (40 * 0.15) = 55 * 9.8 * 6 = 3234 Joules. Power = Work / Time = 3234 / 15 = 215.6 Watts = 0.2156 kW. 1 HP = 746 Watts, so 215.6 / 746 = 0.289 HP. Option A is the closest.