Forms of energy
One of the key aspects you need to learn in this guide is about the different forms of energy.
To make it easier for you to ingest all these ideas, here is a simplified view:
|Kinetic energy||The energy in a moving object is defined as that object’s kinetic energy.|
|Gravitational potential energy||The energy of an object, raised up against the force of gravity is that object’s Gravitational potential energy.|
|Chemical energy||The energy stored in chemical substances and which can be released in a chemical reaction is defined as chemical energy.|
|Electrical energy||The energy transferred by an electric current is called as electrical energy.|
|Nuclear energy||The energy stored in the nucleus of an atom is defined as nuclear energy.|
|Strain energy||The energy produced in an object when it is stretched or compressed is called as strain energy.|
|Internal energy||The energy of an object; the total kinetic and potential energies of its particles is defined as internal energy.|
|Thermal (heat) energy||The energy being transferred from a hotter place to a cooler place, as a result of the temperature difference between them is called as thermal (heat) energy.|
|Light energy||The energy emitted in the form of visible radiation is defined as light energy|
|Sound energy||The energy being transferred in the form of sound waves is called as sound energy.|
Examples of the forms of energy
|Kinetic energy||A moving truck, a running man, a roller coaster, and everything that is moving!|
|Gravitational potential energy||The water stored behind a dam, a fruit hanging on a tree, a man standing on a mountain, etc.|
|Chemical energy||The food we eat, car batteries, crude oil, coal, natural gas, carbohydrates, etc.|
|Electrical energy||The energy flowing through a piece of wire when the switch is pressed ON, etc.|
|Nuclear energy||Energy stored in all radioactive elements such as uranium, americium, plutonium and some radioisotopes such as carbon-14|
|Strain energy||The energy stored in a stretched or compressed spring.|
|Internal energy||The energy stored in the molecules of boiled water, the energy stored in the molecules of a heated iron, etc|
|Thermal (heat) energy||The energy transferred when you warm yourself in front of a fire on a cold day|
|Light energy||A lit candle, an electric bulb, fire crackers, etc|
|Sound energy||A loudspeaker, a guitar, a piano, all produces sound energy.|
Note! There is a VAST difference between internal and thermal (heat) energy! Many students mistake them to be the same! Beware. We have specially simplified the confusing difference for you:
Internal energy: You place a container full of water to boil on a stove. This means you are giving energy to the molecules of water. The energy that is stored in those particles is internal energy.
Thermal (heat) energy: Now, you feel the heat energy escaping from the hot container. This is thermal energy which is getting transferred from the hot container to your cold hands.
Energy stores, energy transfers
Energy can either be stored in an object, or it can be transferred from one object to another.
|Energy stores||Energy transfers|
|Kinetic energy||Sound energy|
|Gravitational potential energy||Thermal (heat) energy|
|Chemical energy||Electrical energy|
|Nuclear energy||Light energy|
The ways in which energy can be transferred from one object to another is given below:
|By a force||When energy is transferred from one object to another, by the means of force, we say that the force is doing work|
|By heating||Thermal (heat) energy always has the tendency to get transferred from a hot place to a cooler one, no matter how good the insulation is!|
|By radiation||Light is transferred from the sun to the earth in the form of electromagnetic radiation such as ultraviolet radiation.|
|By electricity||Often, power-stations use power grids to transfer electrical energy to our homes. These include electrical cables which use electrical energy as a means to transfer electricity.|
When energy changes from one form to another, we can say that it is converted or transformed.
Let us look at an example at a simple energy transformation:
A car accelerating up a hill:
The car is accelerating, so we can say that its kinetic energy is increasing. It is also moving up a hill, so its gravitational potential energy is increasing as well. It produces a lot of sound and heat as it moves.
Hence, to sum it up, here the energy conversion taking place:
Chemical energy -> kinetic energy + gravitational potential energy + thermal energy + sound energy
In examinations, such type of questions may be asked where you need to write energy conversions in the way above.
Conservation of energy
Often when energy is transformed from one form to another, some of the energy ends up as an unwanted form of energy.
Take the previous example where the car is accelerating up a hill; we need the kinetic and the gravitational potential energy but we don’t actually require the sound and heat energy.
However, at a point, the total amount of energy supplied to the car is equal to all the other forms of energy.
1000 J of chemical energy is supplied to the car.
200 J ends up as kinetic energy.
200 J ends up as gravitational potential energy.
500 J ends up as thermal (heat) energy.
100 J ends up as sound energy.
Hence 200 + 200 + 500 + 100 = 1000 J
This is an example of the principle of conversion of energy.
Principle of conversion of energy
In any energy conversion, the total amount of energy before and after the conversion is constant.
This tells us something important about energy:
Energy can never be created or destroyed; the total and final amount of energy remains constant.
As energy is extremely expensive to produce, it must not be wasted and it must be efficiently used.
The idea of energy efficiency is to use cars, electrical appliances, etc. with the least amount of energy being wasted in an undesired form.
Energy is often wasted in the form of thermal (heat) energy, or sound energy. These are common forms of undesired energy.
The efficiency of energy conversion is the fraction of the energy that ends up in the desired form.
How to calculate energy efficiency?
Energy efficiency can be calculated using the formula:
Efficiency = (useful energy output/ energy input) x 100
A tube light is supplied with 100 J of electrical energy and 35 J of useful light energy.
Hence the energy efficiency of the tube light would be:
(35/100) x 100 = 35%
It is interesting to note that energy can be calculated as well!
Here is how we can calculate gravitational potential energy and kinetic energy:
Gravitational potential energy
An object’s gravitational potential energy depends on 2 factors:
- The object’s weight: the greater the weight, the greater the object’s gravitational potential energy.
- The object’s height above the ground level: the greater the height of the object, the greater its gravitational potential energy.
These ideas give out an important formula to calculate gravitational potential energy:
Gravitational potential energy = weight x height
Gravitational potential energy = mg x h
Please consider the vertical height of the object and not the slant height while solving problems based on gravitational potential energy!
The kinetic energy of an object depends on two factors:
- The object’s mass m: the greater the mass, the greater the kinetic energy.
- The object’s speed v: the greater the speed, the greater the kinetic energy.
The ideas above can be combined to give the formula for kinetic energy:
Kinetic energy = 0.5 x mass x speed2
Kinetic energy = 0.5mv2
Please read this part carefully! Students frequently make errors while solving questions related to kinetic energy:
Kinetic energy = 0.5 x mass x (speed2)
Please calculate the ‘square’ of ‘speed’ first and then multiply it with mass and 0.5!
Students often have mistaken the formula for kinetic energy as:
k.e = 0.5 x (mass x speed)2
So you better be careful!
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