Answer
a. Conduction and radiation for glass panes, conduction for the frame, and convection around the edges.
b. Heavy curtains can affect all three of these.
Work Step by Step
a. Heat loss through the glass panes is by conduction and radiation. Heat loss through the frame is by conduction. Heat loss by ventilation around the edges is by convection.
b. Heavy curtains can reduce heat losses from all three mechanisms. The curtains inhibit air circulation, reducing the convection cooling. The curtains are not transparent, lowering the heat loss by radiation. The curtains add another layer of insulation, and also hold a blanket of air between the cold outdoors and the warm indoors. This lowers heat loss by conduction.
