Priyanka B Solutions for Chapter: Sources of Energy, Exercise 3: Assignment-3

Name the device (cell) which directly converts solar energy into electric energy.

On what principle does a solar water heater operate?

Out of two solar cookers, one was covered by a plane glass slab and the other was left open. Which of the two solar cookers will be more efficient and why?

In a solar cooker, the following arrangements are made. Write one function of each arrangement.

(a) The box is made of insulating material such as plastic or wood.

(b) The inner walls of the box are painted black.

(c) The box is covered with a transparent glass sheet.

(d) A plane mirror is hinged at an angle at the top of the box.

A science teacher gave a project to his students to design and prepare a solar cooker by using low cost materials available. The materials used by students were probably thermocol, glass plate, black paper and mirror etc. They also prepared a report about the device. Answer the following questions:

(i) Name the property of solar energy by which solar cooker achieves high temperature.

(ii) Write the role of thermocol and mirror used in constructing the solar cooker.

(i) Why are solar heating devices painted black?

(ii) Name two such devices and state two limitations of these?

Mention why it is not possible to make use of solar cells to meet all our energy needs? State three reasons to support your answer. Also mention three uses of solar cell.

Draw a labelled diagram of a solar cooker. What purpose are served by the blackened surface, glass cover plate and the mirror in a solar cooker? What would happen if the plane mirror of a solar cooker is replaced by a concave glass mirror?