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

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

  1. time in seconds

  2. time in minutes

  3. time in hours

  4. time in days
Reveal answer Fill a bubble to check yourself
C Correct answer
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. 

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

Which of the following is the biggest unit of energy?

  1. Joule

  2. Kilowatt hour

  3. Erg

  4. Electron volt
Reveal answer Fill a bubble to check yourself
B Correct answer
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. 

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

The ratio of SI units to CGS units of energy is

  1. 10$^5$
  2. 10$^6$
  3. 10$^7$
  4. 10$^{-7}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Unit of energy is $ML^2T^{-2}$ 

So in  $CGS$ unit, mass = gram, length = centimeter, time = second.
And in $SI$ unit, mass = kilo gram, length = meter ,time = second.
So ratio of both SI to CGS

=$\dfrac{kg.m^2.s^{-2}  }{g.cm^2.s^{-2}}$

=$\dfrac {1000g.100^2cm^2.s^{-2}}{g.cm^2s^{-2}}$

=$10^7$.

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

The number of joules that is equal in value to 1 kWh is.

  1. $3.6\times 10^8$
  2. $0.36\times 10^4$
  3. $3.6\times 10^5$
  4. $3.6\times 10^6$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

1 kWh is equal to 3.6 $\times$ 10$^{6}$

1 Watt-sec  is a Joule a watt expended for a second.

Because there’s 3600 seconds in an hour,

then 3600 Ws = 1 Wh = 3600 Joules = 3.6 kJ

so 1000 Wh = 1 kWh = 1000 $\times$ 3.6 kJ = 3.6 MJ = 3.6 $\times$ 10$^{6}$

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

Kilowatt hour (kWh) represents the unit of____

  1. power

  2. impulse

  3. mementum

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

The kilowatt hour is a unit of energy equal to $3.6\times 10^6J$. If the energy is being transmitted or used at a constant rate (power) over a period of time, the total energy in kilowatt hours is the power in kilowatts multiplied by the time in hours. so if kWh is unit of energy so none of the option is correct hence option D is the answer.