ENERGY definition | Law of Conservation of Energy – Types of Energy Transfer

It is the quantitative property that must be transferred from one object to another object in order to perform work or to transfer heat. The SI unit of energy is joules. It is derived unit. One joule is equal to the force applying of one Newton through a distance of one meter.

symbols of energy - SI unit - Basic unit - Dimension

Define law of conservation of energy?  

This law states that the total energy of an isolated system is remain constant. It is said that energy is conserved over time. According to this energy can neither be created nor be destroyed. But it transfer from one form to another form.

The amount of energy in any system is determined by the following equation:

Ut = Ui + W + QUt = Ui + W + Q

Ut is the whole internal energy of system.

Ui is the initial internal energy of the system.

W is the work done.

Q is the heat added to or removed from the system.

We also determine the change in internal energy of the system using the equation:


Define law of conservation of energy

Everyday Examples: Law of Conservation of Energy

The everyday examples of the law of conservation of energy:

  1. Water produces electricity. Waterfalls in the form of rain by converting potential energy to kinetic energy. This energy is used to rotate the turbine of a generator that produces electricity. In this process, the potential energy is converted into kinetic energy which can then become electric energy.
  2. When you push the book across the table, the energy from your arm is transferred to the book that causing to move the book.
  3. A cat sitting on the top branch of a tree has what is known as potential energy. If he falls to the ground, his potential energy is converted into kinetic energy.


Types of energy transfer?

Following are methods of different types of energy transfer that we need to learn:

  • conduction
  • convection
  • radiation
  1. Conduction

Heat in the form of thermal energy is transferred by conduction.

Heat is transfer from the hotter end of an object to the cold end of an object by the vibrating of particles in the solid. When the hotter particles start vibration and due to this vibration it collides with the other particles. Through this collision, the heat energy is transfer from one particle to the other particle.

For example

When a saucepan is put on a fire, over time the handle will get hot. This is due to conduction in which the heat from the bottom of the pan will cause the particles to vibrate and then cause all the surrounding particles to vibrate until the handle is hot.

Heat in the form of thermal energy is transferred by conduction

  1. Convection

In gases and liquids the heat energy transfers by convection. Imagine a beaker filled with water being heated from the bottom. When the water particles at the bottom get hot, they start to expand and become less dense. They will rise to the top of the beaker, and other colder water particles will be settled at to bottom of the beaker.

In gases and liquids the heat energy transfers by convection

This process is carried on until the whole water is hot. This constant flow of the fluid due to the expansion and change in particles is called convection. With the passage of time all the fluid reaches a constant temperature.

  1. Radiation

Radiation is different from the other two processes as it doesn’t require particles in its transfer of energy. No medium is required for the propagation of the radiation. The infra-red radiation is a type of electromagnetic radiation. This means that energy is transferred by waves rather than particles. How we feel the heat from the sun on Earth, this is because of radiation. When the waves can pass through the vacuum of space where there are no particles.

transfer of energy through Radiation






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