• Describe the composition of the atmosphere. • Analyse the characteristics of different layers of atmosphere. • Explain the basic working principle of weather instruments with the help of illustrations

1. Composition of the Atmosphere: The atmosphere is composed of a mixture of gases. These include:

   • Nitrogen (78%): This is the most abundant gas in the atmosphere.
   • Oxygen (21%): This is the second most abundant gas in the atmosphere. It is essential for the survival of most life forms.
   • Argon (0.93%): This is a noble gas that is chemically inert.
   • Carbon Dioxide (0.04%): This gas is produced by burning fossil fuels and is a greenhouse gas.
   • Other Gases (0.03%): This includes neon, helium, methane, krypton, and hydrogen, as well as water vapor.

2. Characteristics of Different Layers of Atmosphere: The atmosphere is divided into five main layers. These are:

   • Troposphere: This is the lowest layer of the atmosphere where weather occurs. It extends up to about 8 kilometers at the poles and 18 kilometers at the equator.
   • Stratosphere: This layer sits above the troposphere and extends up to 50 kilometers. The ozone layer, which absorbs and scatters the solar ultraviolet radiation, is in this layer.
   • Mesosphere: This is the layer above the stratosphere, extending up to 85 kilometers. Meteors burn up in this layer upon entering Earth's atmosphere.
   • Thermosphere: This layer is located above the mesosphere and is characterized by high temperatures. It extends up to 600 kilometers. The Northern and Southern Lights occur in this layer.
   • Exosphere: This is the outermost layer of the atmosphere. It extends from the top of the thermosphere up to 10,000 kilometers.

3. Working Principle of Weather Instruments:

   • Thermometer: It measures the temperature of the atmosphere. The basic principle behind a thermometer is that liquids expand when heated and contract when cooled.
   • Barometer: It measures atmospheric pressure. It works on the principle that the pressure exerted by the atmosphere at a given point is directly proportional to the height of the fluid column above that point.
   • Hygrometer: It measures the moisture content in the atmosphere. It works on the principle that different materials absorb water to different extents.
   • Anemometer: It measures wind speed. The basic principle behind an anemometer is that the wind speed is proportional to the rotational speed of the cups.
   • Rain Gauge: It measures the amount of rainfall. It works on the principle of a simple collection and measurement.

For illustrations, you may refer to any standard textbook or online resources.