Question

Why the heat gets trapped up in solar cooker

Answer 1

Enclosed spaces in the cooker into which the sun rays enter through a transparent material such as glass or plastic heats up due to green house effect. ... Heat trapped within a solar box cooker is lost through conduction, convection and radiation

Answer 2

The glass in the solar cooker allows all kinds of radiations to pass through it. The incoming sunlight contains infrared radiation at shorter wavelength (near the visible red)and therefore its behaviour is not different from that of visible light; except that they are invisible to human eye. The inside of the solar cooker absorbs those radiations, gets heated and then emits infrared radiation of larger wavelength than that absorbed. This larger wavelength infra red radiation is not able to pass through the glass and gets trapped in the cooker which heats up the inside of the cooker and is responsible for cooking of the food.