Answer question numbers 3(a) to 3(d) on the basis of your understanding of the following paragraph and the related studies concepts.

The Tehri dam is the highest dam in India and one of the highest in the World. The Tehri dam withholds a reservoir of capacity $4.0 \text{ km}^3$ and surface area $52 \text{ km}^2$. It is used for irrigation, municipal water supply and the generation of 1000 MW of hydro electricity.

The Tehri Dam has been the object of protests. Environment activist Shri Sunder Lal Bahuguna led the "Anti Tehri Dam Movement" from 1980s to 2014. The protest was against the displacement of town inhabitants and environmental consequences of the weak ecosystem. The relocation of more than 1,00,000 people from the area has led to protracted legal battles over resettlement rights and ultimately resulted in the delayed completion of the project.

(a) How is hydropower harnessed?

(b) Define 1 MW.

(c) Mention two disadvantages of constructing Tehri Dam.

(d) What happens when water from great heights is made to fall on blades of turbine?

(a) Hydropower is harnessed by constructing high dams across rivers to obstruct the flow of water and collect it in large reservoirs. The potential energy of this stored water at a height is converted into kinetic energy as it is allowed to fall from a height through pipes. This falling water rotates the blades of a turbine connected to an electric generator, which converts mechanical energy into electrical energy.

(b) $1 \text{ MW}$ (Megawatt) is a unit of power equal to one million watts ($10^6 \text{ W}$ or $10^6 \text{ J/s}$). It represents the generation or consumption of $10^6$ Joules of electrical energy per second.

(c) Two major disadvantages of constructing the Tehri Dam are:

1. Social Problems: Displacement of a large number of local inhabitants and town residents without proper rehabilitation and resettlement.
2. Ecological Problems: Destruction of vast natural ecosystems, loss of rich biodiversity, and submergence of fertile agricultural land and forests under the reservoir water.

(d) When water from great heights falls on the blades of a turbine, its potential energy is converted into kinetic energy. This kinetic energy is transferred to the turbine blades, causing them to rotate rapidly. The rotating turbine turns the shaft of an electric generator, converting mechanical energy into electrical energy.