In this experiment, you will use a lightweight thread suspended from a clamp to detect convection currents near different hot objects. You hangs the thread ...

(a) The thread deflects upward (and slightly toward the hot plate). [1]

(b) The hot plate heats the air beside it. This warm air expands and becomes less dense than the surrounding cooler air. [1] The warm air rises (convection), creating an upward air current that pushes the thread upward. Cooler air moves in from the side to replace the rising warm air, which also pulls the thread slightly toward the plate. [1]

(c) Convection. [1]

Convection is the transfer of thermal energy through the bulk movement of a fluid caused by density differences. The heated air near the plate is less dense and rises, creating a current.

(d) When the plate cools to room temperature, the thread hangs vertically with no deflection. [1] There are no convection currents because there is no temperature difference between the plate and the surrounding air, so no density difference to drive air movement.

(e) Measure the vertical distance from the base to the top of the hot plate in Fig. 62.1 using a ruler. The height is approximately 2.5 cm on the printed diagram (accept any reasonable measurement with a unit). [1]

(f) The thread is very lightweight and may be affected by draughts or unrelated air currents in the room. [1] It is also difficult to measure the exact angle or magnitude of the deflection precisely.