Name the reaction responsible for large energy production in the sun.

Write the characteristic features of the microorganisms which help in the production of biogas in a biogas plant.

In a hydroelectric power plant,more electrical power can be generated if water falls from a greater height because:

The nuclear fuel in the sun is:

What is the use of a glass sheet in solar heating devices?

$(a)$ Describe the structure of a windmill.
$(b)$ Give one example to illustrate that energy from a windmill was used in the past to do mechanical work.