[Explain] List out three methods of soil conservation

All those measures that include help in protecting the earth from destruction and exhaustion are known as soil conservation. In our country, soil erosion has been continuing over for such a long time that it has assumed alarming proportions.

Following methods are normally adopted for conserving soil:

1. Afforestation:

One of the best ways to conserve soil is to increase the area under forests. Undiscriminating trees cutting should be stopped and efforts should be made to plant trees in new areas. 20 to 25 per cent, as they say, is the minimum area of forest land for the whole country which is considered healthy for soil and water conservation. Nevertheless, it was raised to 33 per cent in the second five-year plan; the proportion being 20 per cent for the plains and 60 per cent for hilly and mountainous regions.

2. Checking Overgrazing:

Grazing is very important. But overgrazing of forests and grasslands by animals, especially by herds and flocks of sheep, goats, should be properly checked. One can earmark separate grazing grounds. Alternate fodder crops should be grown in larger quantities. 

3. Constructing Dams:

One of the scientific methods to check soil erosion. Soil erosion which happens maximum by river floods can be avoided by constructing dams across the rivers. Water speed can be checked and it considerably saves soil from erosion.

4. Changing Agricultural Practices:

We can save a lot of our valuable soil by bringing about certain changes in our agricultural practices. Roughly the context is described below:

(i) Crop Rotation:

As the name suggests, it is rotating crops. In India, peasants grow a particular crop in the same field year after year. This practice takes away certain elements from the soil, making it infertile and exhausted rendering it unsuitable for that crop. 

(ii) Strip Cropping:

Parallel to one another, crops may be cultivated in alternate strips. Some strips may be allowed to lie fallow while in others different crops may be sown e.g., small tree crops, grains, grass legumes, etc. Numerous yields ripen at diverse times of the year and are harvested at intervals. This very method gives surety that at no time of the year the entire area is left bare or exposed.

(iii) Use of Early Maturing Varieties:

Primary budding varieties of crops take really very less time to mature. Thus putting lesser pressure on the soil. In this way it can help in reducing the soil erosion.

(iv) Contour Ploughing:

Technical methods, one can say. Ploughing is done at right angles to the hill slope, following the natural contours of the hill. It makes the ridges and furrows break the flow of water down the hill. As gullies are less, this prevents excessive soil loss. It is likely to develop and reduce run-off so that plants receive more water. 

(vi) Terracing and Contour Bunding:

Claims to be one of the oldest methods of soil conservation. Terracing and contour bunding across the hill slopes are very effective. It is done by cutting hill slope into a number of terraces having horizontal top and steep slopes on the back and front. 

(vii) Checking Shifting Cultivation:

Shifting cultivation method is mainly used by tribal. We can persuade tribals to switch over to settled agriculture by checking shifting cultivation. Arrangements for tribal resettlement can help to make them understand the new way of cultivation. The new method involves the provision of agricultural implements, residential accommodation. 

(viii) Ploughing the Land in Right Direction:

Ploughing the land in a perpendicular direction to wind direction. This also reduces wind velocity and protects the topsoil from erosion.

[Explain] Define absolute refractive index of a medium.

Hint: The speed of light depends upon the medium in which it is traveling. And apart from this, there are various other factors that determine the speed of light. Knowing all the factors will help us to define the absolute refractive index.

The absolute refractive index is expressed with the help of the symbol n.
The refractive index of a medium depends upon the refractive index of the surrounding. By surrounding we mean the surrounding in which the light ray is passing from into the medium. The Refractive index also depends upon optical density, the wavelength of the light, and temperature. 

Note:

> The value of the refractive index of light determines the extent to which the light will be refractive when entering or leaving the substance. According to the laws of nature, no substance can travel faster than the speed of light in a vacuum. Those materials with large indices of refraction are known as optically dense media.

> Refractive index is directly proportional to the optical density. It is considered inversely proportional to the wavelength of light.

[Explain] What is the formula for recoil velocity of the gun ?

After firing the bullet, the bullet moves forward with a large momentum and the gun moves backward with an equal momentum. 

Let m and M be the masses of bullet and gun,respectively. If v and V are the velocities of the bullet and gun, respectively after the firing then:- 

0= mv+ MV 

Therefore V=-mv/M 

The negative sign indicates that the gun moves in a direction to that of the bullet.

[Explain] How is plaster of paris prepared? what is its chemical formula and chemical name? 

Calcium sulphate with half a molecule of water per molecule of the salt (hemi-hydrate) is called plaster of paris (plaster of paris).

It is prepared by heating gypsum (CaSO4.2H2O) at 120°C in rotary kilns, where it gets partially dehydrated.

Plaster of paris is a white powder, which when mixed with water sets into a hard mass as crystals of gypsum are produced with evolution of heat. Hence it is used in setting of plaster for fixing broken bones. It is also used in making several decorative items, toys and chemical plugging 

[Explain] What is sedimentation, decantation and filtration ?

Settling down of heavier insoluble particles/ solids from a mixture is called sedimentation. Like mud settles from muddy water.

Decantation is pouring out of upper clear layer of liquid into another container to separate two immiscible liquids. Like draining oil from a mixture of oil and water after allowing the two to separate and form distinct layers

Filtration is the process of separating insoluble impurities from a solution. When a solution is passed through a filter, particles with pore size bigger than that of the filter are retained while others pass through. Like filtering mud from muddy water

(Image to be added soon)