Why is the copper tube of a solar water heater painted black from outside ?

Why is the box of a solar cooker painted black from inside ?

Why are solar heating devices painted black form inside ?

(a) With the help of a labelled diagram, explain the construction and working of a solar cooker. (b) Why is the solar cooker box painted black from inside ? (c ) Why is the solar cooker box covered with a glass sheet ?

A solar water heater cannot be used to get hot water on :

Two students made box-type solar cookers separately. They both painted the insulated box with black colour from inside, the cooking pots were painted black from outside, and a plane mirror reflector was also attached. One of the students covered the solar cooker box with a transparent glass sheet but the other student covered the solar cooker box with a transparent plastic sheet. Which of the two solar cookers will be more efficient and why ?