Tag: the essence of change

Questions Related to the essence of change

The correct sequence of energy changes in hydroelectric power station is:

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. Kinetic to potential to mechanical to electrical

  2. Potential to kinetic to mechanical to electrical

  3. Potential to electrical to mechanical

  4. Potential to electrical to kinetic to mechanical

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Correct Option: A
Explanation:

First of all moving water is stored against a dam and then it is allowed to fall on turbine and then as turbine rotates it will produce electricity.

So sequence of energy conversion is 
Kinetic to potential to mechanical to electrical.
Hence option A is best possible.

Electric heater converts :

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. electric energy into chemical energy

  2. chemical energy into electric energy

  3. heat energy into electric energy

  4. electric energy into heat energy

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Correct Option: D
Explanation:

An electric heater is an electrical device that converts electric current to heat. The heating element inside every electric heater is an electrical resistor, and works on the principle of Joule heating: an electric current passing through a resistor will convert that electrical energy into heat energy.

The height of water in a dam reduces by $20  m$, which is used to generate electricity. The water further fell by $10  m$ into the tunnel to strike the turbine plates. If the volume of water is ${10}^{4}  {m}^{3}$, find the hydel energy generated. Assume all the potential energy of the water being converted into electricity. Take $g = 10  m{s}^{-2}$.

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. 2000 MJ

  2. 200 MJ

  3. 1000 MJ

  4. 500 MJ

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Correct Option: A
Explanation:

The potential energy of the stored water is converted into kinetic energy which is then converted into electrical energy.
The potential energy of water $= mgh$        ...... (1)
The volume of water $= 10000  {m}^{3}$.
The mass of water $=$ volume $\times$ density $= 10000 \times 1000 = {10}^{7}  kg$.
Also, the depth of water $= 20  m$.
$\therefore$ The height of CG of stored water $= 10  m$.
The total height through which water falls $= 20  m$.
Substituting it in (1), we get potential energy of water $= {10}^{7} \times 20 \times 10 = 2000  MJ$.