Table of Contents
Work is said to be done when a force is applied on a body and the body displaces from its initial position.
w = F x s
Types of Work (Positive, Negative, Zero)
- Positive Work Done: When the displacement is in the direction of the force applied. Ex: A boy pulls an object towards himself.
- Negative Work Done: If the displacement is in the opposite direction of force applied. Ex: When you’re pushing an object along the floor
- Zero Work Done: If the displacement is perpendicular to the force applied, or either of the two is zero. Ex: a man pushes a wall
The ability or capacity to do work is called Energy.
Note: Both Work and Energy are scalar quantity and have the same SI, CGS units, as mentioned below
- Scalar quantity
- SI Unit: J
- CGS Unit: Erg
|1 kJ||103 J|
|1 cal||4.2 J|
|1 Erg||10-7 J|
|1 ev||1.6 x 10-19 J|
- Heat Engine: Heat energy to Mechanical energy
- Solar Cell: Solar energy to Electrical energy
- Microphone: Sound(acoustical) energy to Electrical energy
- Loudspeaker: Electrical energy to Sound energy
- Battery: Chemical energy to Electrical energy
- Candle: Chemical energy to Light energy
- Electric Motor: Electrical Energy to Mechanical Energy
- Sitar: Mechanical Energy to Sound Energy
- Electric Bulb: Electrical energy to Light Energy
Types of Energy
1. Kinetic Energy
The energy possessed by a body due to its motion, is called its kinetic energy.
KE = (mv2) / 2 = p2 / 2m
- Ex: A collision of pool balls
Work Energy Theorem: w = change in kinetic energy
Potential Energy (U)
The energy possessed by a body due to change in its position or shape, is called potential energy.
- Ex: A coiled spring, Water behind a dam.
The sum of the potential energy and Kinetic energy of an object is known as mechanical energy.
Gravitational Potential Energy
When an object is raised through a certain height above the ground, its energy increases. The energy is called Gravitational Potential Energy.
U = mgh
Various forms of Energies
- Internal Energy: The energy in a system arising from the relative positions and interactions of its parts.
- Heat Energy: Energy possessed by a body due to its temperature, is called heat energy.
- Electrical Energy: The energy which is caused by the movement of the electrons from one place to another.
- Chemical Energy: The energy absorbed or released during a chemical reaction is called chemical energy.
- Nuclear Energy: The energy absorbed or released during a nuclear reaction is called Nuclear Energy.
The rate of doing work by a body is called power.
P = w / t
- SI Unit: W (Watt)
- Scalar Unit
- 1 kw = 3.6 x 106 J = 3.6 megajoule (mJ)
- 1 HP (Horse Power) = 746 W
Energy vs Power
Energy is the amount of work done whereas Power is the rate of doing work.
Law of Conservation of Energy
Energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another.
- The total energy of an isolated system remains constant, it is said to be conserved over time.
1. Renewable Energy Resources
The energy resources which are naturally replenished on a human timescale.
- Ex: Solar, Wind, Hydroelectric, Biomass, Geothermal, etc.
2. Non-renewable Energy Resources
The resource that does not renew themselves at a sufficient rate for sustainable economic extraction in meaningful human time-frames.
- Ex: Petroleum, Coal, Natural gas, Nuclear Energy, etc.
Conventional Sources of Energy
- Fossil Fuel: A natural fuel such as coal or gas, formed in the geological past from the remains of living organisms.
- Thermal Power Plant: A power plant in which heat energy is converted to electric power.
- Hydro-power Plant: Power plants which converts the potential energy of falling water into electricity. Electricity thus produced is called hydro electricity.
- Wind Energy: The energy possessed by the wind is due to its high speed. Wind turbines converts wind energy into electrical energy.
Wind vs Air: Moving air is called wind.
Non-Conventional Sources of Energy
- Geothermal Energy: The heat from interior of the earth under certain favourable conditions that are created by the natural processes. This is known as geothermal energy.
- Solar Energy: It is radiant light and heat from the Sun that is harnessed using a range of ever-evolving technologies such as solar heating, photovoltaics, solar thermal energy, solar architecture, molten salt power plants and artificial photosynthesis.
Solar Cell (photovoltaic cell)
A solar cell is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.
- Made from semiconductors like Si, Ga, Ge, etc.
Tidal power or tidal energy is a form of hydropower that converts the energy obtained from tides into useful forms of power, mainly electricity.
- Tide: The rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of Earth.
- High Tide: The natural tide at its highest level for a particular tidal cycle at a certain place.
- Low Tide: The tide at its lowest level for a particular tidal cycle at a certain place.