Unit 21: Space & Environment

Sun: The Sun is the greatest source of light, heat and other forms of electromagnetic (E.M) waves.

Nuclear Fusion in the Sun: Nuclear fusion takes place at the core of the Sun, in which hydrogen atoms are fused together to form helium, resulting in a tremendous increase in the temperature of the Sun (in millions of degree celsius).

Generation of Energy: This releases a massive amount of energy which reaches the Earth in the form of light and heat. The energy released from the Sun travels through space in the form of various types of radiations such as infrared, heat, sunlight and ultraviolet radiations.

Orbital Distance and Solar Energy: Those planets that are closer to the Sun have smaller orbital distance and those located at a far away distance from the Sun have large orbital distances. Orbital distance plays a vital role in determining the amount of solar energy received by each planet.

Effect on Surface Temperature: Surface temperature depends on factors like distance from the Sun, atmospheric composition, and greenhouse effects. For example, Venus has an extremely high surface temperature due to its thick, heat-trapping atmosphere, while Mars is much colder due to its thin atmosphere and greater distance from the Sun.

Answer: Cyclones refer to heavy storms containing fast and spinning winds forming around low air pressure area. The phenomenon of convection is responsible to develop these cyclones. The convection takes place due to rise of the warm air (being lighter) as compared to the heavier cool air that moves down. Due to rise in the warm air, more air rushes in to take its place, which creates the spinning effect. The cyclone grows stronger and bigger due to the movement of air.

Warm Ocean Waters: Formation of cyclones occurs over warm oceans where temperature of the sea surface is very high (27°C or 300 K). The air above the warm water is heated, becomes less dense and rises rapidly. This movement of the warm air in the upward direction creates an area of low pressure at the surface.

Rising Air and Condensation: The rising warm air moves to low air pressure areas, causing the air to expand. The clouds are formed due to the moisture in the air and as a result, heat is released into the surrounding air. Due to this heat, the air becomes even warmer and it rises even faster.

Formation of a Low-pressure Centre: As the warm air keeps rising, warmer, moist air from the surrounding areas rushes in. Because the Earth is spinning, this moving air starts to spin around the low-pressure area. This effect is called the Coriolis effect. In the northern hemisphere, the air spins anticlockwise, while in the southern hemisphere, it spins clockwise.

Development of a Cyclonic System: As more warm air keeps getting pulled into the storm, the rising and spinning of the air becomes even stronger. The cyclone keeps growing as long as it has warm, moist air from the ocean.

Energy Dissipation: Cyclones start to weaken when they move over land or colder water because they can no longer get warm, moist air, which acts like fuel for the storm. Without this energy, the storm loses its strength, the winds become weaker, and the cyclone slowly fades away.

Answer: The radiation that exists around us all the time is known as background radiation. It is the constant, low-level ionizing radiation present in the environment from both natural and human-made sources.

(a) Radon Gas: Radon gas is an alpha emitter. Radon gas from the ground can seep into homes, especially basements, and contribute to natural background radiation. It is invisible, odourless, and radioactive.

(b) Rocks and Buildings: Natural radioactivity can be found in building materials, including decorative rocks, stones and bricks. Heavy radioactive elements, such as uranium and thorium, occur naturally in rocks in the ground. Uranium decays into radon gas.

(c) Food and Drink: Food and water contain small amounts of naturally occurring radioactive isotopes, such as potassium-40 and carbon-14. These isotopes are absorbed by plants and animals and enter the human body through consumption.

(d) Cosmic Rays: The Sun and other stars emit an enormous number of cosmic rays including protons. Some of these enter the Earth's atmosphere at high speeds. When they collide with molecules in the air, they lead to the production of gamma radiation.

Human Activities: Human activities, such as medical procedures (X-rays, CT scans), nuclear power plants, and past nuclear testing, also contribute to background radiation.

Answer: Radiation exposure happens when someone comes into contact with radiation, which is a type of energy. A small amount of radiation is usually safe, but too much exposure can harm our bodies by damaging cells.

(i) High exposure to radiation in a short time can cause radiation sickness, with symptoms like nausea, vomiting, fatigue, and organ damage.

(ii) Long-term exposure to low levels of radiation increases the risk of cancer, especially in organs like the lungs, thyroid, and bones.

(iii) Radiation can damage DNA, leading to genetic mutations that may affect future generations.

(i) Protective Wear: Protective wear is used to stay safe while using radiation for useful purposes.

(ii) Limited Exposure: Exposure to radiation should be limited to reduce its harmful effects.

(iii) Safe Storage and Handling: Radioactive materials should be stored or handled safely to avoid accidents such as leaks and spills.