Work and Energy

Tutormate > CBSE Syllabus-Class 9th Physics > Work and Energy

02 Energy

ENERGY

Energy of a body can be defined as its capacity to do work.
The amount of energy possessed by a body is equal to the amount of work it can do when its energy is released.
It is a scalar quantity.
Various types of energy can never be created nor destroyed but can only be transformed from one form to another.
For example, physical or chemical resources are processed to generate energy in a generating power station which is further used to provide light or heat energy for domestic or industrial purposes.
Energy is the strength to do any kind of physical activity. People compare two persons A & B and conclude that A has more energy than B based on their capacities to do physical activity.

UNIT OF ENERGY

Since energy is measured by the amount of work that a body can perform, the units of work and energy are the same.
SI unit of energy is joule (J) or Newton metre.

Joule

One joule of energy is the energy required to do 1 J of work. It is given as

$1 joule = 1 newton \times 1 metre or J = 1 Nm$

1 kilo joule = 1 kJ = 1000 J

Thus, when a certain amount of force (Newton) is applied to an object and it moved certain distance (meters), then the energy applied is said to be Joules (Newton-meter).

COMMERCIAL UNIT OF ENERGY

The commercial unit (or trade unit) of energy is kilowatt-hour.

Kilowatt-hour (kWh)

It is defined as the electric consumed by an appliance of power 1000 watt in one hour.

1 kWh = 3.6 \times 10^{_{}^{6}} J

1 Kilowatt-hour (or) of electrical energy is commonly known as ‘1 unit’ of electricity.

DIFFERENT TYPES OF ENERGY

There are various forms of energy. Mechanical energy (kinetic and potential), sound energy, heat energy, light energy, chemical energy, nuclear energy, electric energy, magnetic energy, solar energy, etc.

FORMS OF ENERGY