A styrofoam sheet of thickness 5 cm and area 0.25 m2 has a temperature difference of 40°C between its inner and outer surfaces. The rate of heat flow through the sheet [thermal conductivity is 0.01 J/(s m K)] is:
1
2.0 J/s
2
1.0 J/s
3
3.0 J/s
4
4.0 J/s