The area directly above a light bulb is warmest because of convection.

The area directly above a light bulb is warmest because of convection.

• A. The areas to the sides of the light bulb are warmest because of conduction.
• B. The areas to the sides of the light bulb are warmest because of convection.
• C. The area directly above the light bulb is warmest because of conduction.
• D. The area directly above the light bulb is warmest because of convection.

Answer: (D)

Convection is the key idea here: heat transfer by moving fluid. When the light bulb heats the surrounding air, the air near the hot surface becomes less dense and rises. That upward flow of warm air tends to collect just above the bulb, so the area directly above ends up warmer than the sides. Conduction isn’t the main player in air around an uncontained bulb because air is a poor conductor, so heat transfer by contact isn’t driving the temperature pattern there. Radiation is happening too, since the bulb emits heat in all directions, but the steady rise of heated air above the bulb concentrates heat upward, making the region above the bulb the warmest.

Convection is the key idea here: heat transfer by moving fluid. When the light bulb heats the surrounding air, the air near the hot surface becomes less dense and rises. That upward flow of warm air tends to collect just above the bulb, so the area directly above ends up warmer than the sides.

Conduction isn’t the main player in air around an uncontained bulb because air is a poor conductor, so heat transfer by contact isn’t driving the temperature pattern there. Radiation is happening too, since the bulb emits heat in all directions, but the steady rise of heated air above the bulb concentrates heat upward, making the region above the bulb the warmest.