Sources of Energy

Que 1. Which part of the solar cooker is responsible for greenhouse effect?

Ans. The glass sheet in the solar cooker creates a greenhouse effect. Glass sheet has a property that allows the infra-red rays of shorter wavelength from the Sun to get in the device but does not allow the infra-red rays of longer wavelength to leave the solar heating device. Therefore, heat energy is trapped inside the heating device.

Que 2. Though wood is a renewable source of energy, but the use of wood as a fuel is not a wise decision. Explain.

Ans. Wood is a renewable source of energy. It is obtained by cutting trees. A new plant sapling usually takes more than 15 years to grow and mature into a tree. Therefore, replenishment of cut down trees takes a very long time. Cutting down of trees causes depletion of the forests leading to imbalance in nature. Due to unsuitable air and the above reasons, usage of wood as a source of energy is not a wise decision

Que 3. Wavelength of radiation incident on a surface is 850 nm. Will the surface become visible when exposed to this radiation? Explain.  

Ans. As we know, the range of wavelength of visible radiation is from 400 nm to 700 nm. The radiation having wavelength greater than 700 nm is termed as infra – red radiations which only produces warmth, so the wavelength of radiation 850 nm cannot be visible.