Effect of Radiation on Temperature Measurement

From this energy balance we see that the temperature indicated by the thermometer is not the true gas temperature but some radiation-convection equilibrium temperature. Very large errors can result in temperature measurements if this energy balance is not properly taken into account. Radiation shields are frequently employed to alleviate this difficulty. 

A mercury-in-glass thermometer having e 0.9 hangs in a metal building and indicates a temperature of 20°C. The walls of the building are poorly insulated and have a temperature of 5°C. The value of h for the thermometer may be taken as 8.3 W/m °C. Calculate the true air temperature. 

---