In which of the following, heat loss is primarily not due to convection?
[amp_mcq option1=”Boiling water” option2=”Land and sea breeze” option3=”Circulation of air around blast furnace” option4=”Heating of glass surface of a bulb due to current in filament” correct=”option4″]
This question was previously asked in
UPSC CDS-2 – 2018
A) Boiling water: Heat is transferred throughout the water by convection currents.
B) Land and sea breeze: These are atmospheric movements caused by differential heating, a classic example of convection.
C) Circulation of air around blast furnace: Hot air rises and cooler air sinks, setting up convection currents around the furnace.
D) Heating of glass surface of a bulb due to current in filament: The filament of an incandescent bulb gets extremely hot due to the electric current. Heat is transferred from the filament to the surrounding space (including the glass envelope). If the bulb is evacuated, there is no medium for convection inside. Even if filled with an inert gas, the primary mode of heat transfer from the very hot filament across the gap to the glass envelope is thermal radiation. The glass surface then heats up by absorbing this radiation. While there might be some conduction through the support wires and subsequent convection/radiation from the outer glass surface, the initial transfer from the filament to the glass inside the bulb is significantly by radiation, not primarily convection.