Shailesh Koirala 
It is also known as theory of natural selection. Charles Robert Darwin was (1809- 1882) an English naturalist published his famous book “ The origin of species by natural selection” in 1859. This theory is based on a mass of accurate observations and prolonged experiments. This theory led the whole scientific world to believe in … Read more
GROUNDWATER Ground water by definition is the freely moving water that occurs below the ground water table. The ground water is the level below which the geological formation is fully saturated. Ground water is considered as the major part of the sub-surface water. Water in the rock mass is the integrated part of hydrological cycle. … Read more
The earth is surrounded by a thick layer of air. This thick layer of air is called the atmosphere. The thick layer of air that surrounds the earth’s crust is called atmosphere. The biosphere of the earth consists of three different spheres, which are: hydrosphere, lithosphere and atmosphere. The atmosphere consists of different types of … Read more
When a solid object is immersed in a fluid, an upward force acts on it. The magnitude of the force is given by Archimede’s principle. This principle was propounded by Archimedes (287- 212 BC), a famous Greek scientist. Archimede’s principle states , “ When a body is partially or wholly immersed in a fluid, it … Read more
The disorder in which a person cannot see nearby or distant objects clearly is called defect of vision. There are two most common defects of vision. They are: a)Myopia It is the defect of vision in which a person can see nearby objects clearly but cannot see distant objects. It is also called short sightedness … Read more
It is a device that converts high voltage AC to low voltage AC of the same frequency and vice versa. It works on the principle of mutual induction, i.e., whenever the current (magnetic flux) through a coil changes, an e.m.f. is induced in the neighbouring coil. According to this principle, when the electric current in … Read more
It is a metallic silicate of various metals. It is a hard, transparent, amorphous and super-cooled liquid. It is an important industrial material which is used in our daily life. It is prepared by heating a mixture of silica, sodium carbonate and calcium carbonate in a furnace. Characteristics It is a hard, transparent homogenous mixture … Read more
It is one of the artificial methods of asexual reproduction. In this method, the roots are developed on the stem while the stem is still attached to the parent plant. This method is commonly used in jasmine, magnolia, strawberry, raspberry, etc. Many plantlets can be produced in a short period of time. It is induced … Read more
It is one of the artificial methods of vegetative propagation. In this method, the root system of one plant is combined to the shoot system of another plant to obtain a plant of superior quality. The plant whose root system is taken is called stock and whose shoot system is taken is called scion. This … Read more
It is a common method of reproduction in lower plants and animals. A single organism is involved in this method i.e. capable of reproduction. The method of reproduction where a single parent is involved and there is no fusion of male and female gamete is asexual reproduction. Sex cells or gametes are not involved. The … Read more