Minimum velocity of wind required for a functional windmill is about:

State any two impacts on the environment caused due to the increase in energy demand. Suggest any two steps to reduce energy consumption.

Name the major fuel component of biogas. What are its other combustible components? Draw a simple labelled diagram of a fixed dome type biogas plant. What is the use of the residual slurry and why?

The temperature difference required up to a water level difference of $1000 \,m$ for operating an Ocean Thermal Energy Conversion $(OTEC)$ system is: (in $^{\circ} C$)

Hydroelectricity generated at a dam may be considered to be another form of solar energy. Why?

There are about $50$ teachers in a school and most of them come to school by their own cars. Many of the teachers come from the same place but everyone prefers to come to school by his/her own car.
Answer the following questions based on the above information:
$(a)$ Do you think that their practice of commuting to school is environmental-friendly? Give one suggestion. Justify your answer.
$(b)$ In what other two ways can we become environmental-friendly?