Tag: work and energy

Questions Related to work and energy

A certain household has consumed $250$ units of energy during a month. How much energy is this in joule ?

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. $9 \times 10^8:J $

  2. $10 \times 10^8:J $

  3. $9 \times 10^7:J $

  4. $9 \times 10^{-8}:J $

Show answer
Correct Option: A
Explanation:

Energy consumed in a month
$=250 : units = 250 : kWh$
$= 250 \times 3.6 \times 10^6 = 9 \times 10^8:J $

Kilowatt-hour ($kWh$) represents the unit of :

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. power

  2. impulse

  3. momentum

  4. none of these

Show answer
Correct Option: D
Explanation:

The kilowatt-hour ($kWh$) is a unit of energy equivalent to one kilowatt ($1\  kW$) of power expended for one hour ($1\  h$) of time.


State whether the given statement is True or False :
Kilowatt hour is the unit of power.
physics energy and its forms idea of energy introduction to work and energy work and energy

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

False
because,The kilowatt-hour (kWh) is a unit of energy equivalent to one kilowatt (1 kW) of power expended for one hour (1 h) of time.

The commercial unit of measurement energy is 

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. Watt -Hour

  2. Kilowatt

  3. Kilowatt hour

  4. Megawatt

Show answer
Correct Option: C
Explanation:

The commercial unit of measurement energy is Kilowatt hour.

The power supply in our home is measured in Kilowatt hour units.

$1\ kW$ is equal to :

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. $1000\ watt$

  2. $10^{-3}\ mega\  watt$

  3. $A$ and $B$ both

  4. neither $A $ nor $B$

Show answer
Correct Option: C
Explanation:

$1000\ W= 1\ kW$
$1000 \ kW= 1\ MW$

The unit kWh represents

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. power

  2. momentum

  3. energy

  4. force

Show answer
Correct Option: C
Explanation:

This is unit of energy.If the energy is being transmitted or used at a constant rate over a period of time, the total energy in kilowatt hours is the power in kilowatts multiplied by the time in hours.

Which of the following is different from the others?

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. Joule

  2. Kilowatt hour

  3. Erg

  4. Watt

Show answer
Correct Option: D
Explanation:

Joule, kilowatt Hour and Ergs are different units of the physical quantity Energy.


Watt is a unit of Power

Hence, Option D is correct

Number of kilowatt-hours = $\displaystyle \frac{volt \times ampere \times  \,...........}{1000}$

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. time in seconds

  2. time in minutes

  3. time in hours

  4. time in days

Show answer
Correct Option: C
Explanation:

Power, $P=VI$

1 kilowatt-hour means $P=1 kW=1000 W$ and time $t=1 hour$
As kWh is the unit of electrical energy so $1 kWh=VIt/1000$. 
Thus, time will be in hour. 

Which of the following is the biggest unit of energy?

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. Joule

  2. Kilowatt hour

  3. Erg

  4. Electron volt

Show answer
Correct Option: B
Explanation:

Since, we know that SI unit of energy is represented by Joule. Hence, let us convert all the different units in the form of Joules. 


Option A- 
1 Joule= $1\quad Joule\quad =\quad [kg]{ [\frac { m }{ s } ] }^{ 2 }$

Option B-
$kWh\quad =\quad 1000W\times 3600s\quad =\quad 3600000\quad W\times s$

As we know that 1 Ws = 1 Joule

So 1 kWh= 3600000 Joules

Option C- 
$1\quad Joule\quad =\quad [kg]{ [\frac { m }{ s } ] }^{ 2 }=\quad \left[ 1000\quad gm \right] \left[ \frac { 100\quad cm }{ 1\quad s }  \right] \left[ \frac { 100\quad cm }{ 1\quad s }  \right] \ S0,\quad 1\quad Joule\quad =\quad { 10 }^{ 7 }gm\frac { { cm }^{ 2 } }{ { s }^{ 2 } } \quad =\quad { 10 }^{ 7 }\quad erg\ So,\quad 1\quad erg\quad =\quad { 10 }^{ -7 }Joule$

Option D- 
Electron Volt is the unit of energy in terms of change in energy for one electron in the potential difference of one volt. So, mathematically it is-

$1\quad ev\quad =\quad Charge\quad of\quad one\quad electron\quad \times \quad 1\quad Volt\quad =\quad 1.6\quad \times { 10 }^{ -19 }Coloumb\quad \times \quad 1\frac { Joule }{ Coloumb } \ So,\quad 1\quad ev=\quad =\quad 1.6\quad \times { 10 }^{ -19 }Joule$

Hence, Option B is the largest unit of energy and hence it is practically used in everyday life of electric consumption. 

How many joules are there in one kilowatt hour?

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. ${35 \times 10 ^6 }$ J

  2. ${3.5 \times 10 ^6 }$ J

  3. ${36 \times 10 ^6 }$ J

  4. ${3.6\times 10 ^6 }$ J

Show answer
Correct Option: D
Explanation:

As, $1kW=1000W ; 1hr=3600s$
$1kWh=1000Wh=3600000=3.6\times10^6Ws=3.6\times10^6J$