Question

Why are solar cooker covered with a glass plate

Answer 1

Glass covers function to trap the heta radiations inside the box. ... The same radiations are reradiated in longer wavelengths, which fail to get refracted out of the glass cover. Subsqeuently, the heat radiations get trapped inside the box & hence the temperature rise inside the box.

Answer 2

This is because it works on the principle of greenhouse effect. When the sunlight enters the cooker, the glass trap the heat energy and so it cooks the food.