Interactive Lecture Demonstration: Convection current in a liquid

by Erees Queen Macabebe and Ivan Culaba
Physics Department, Ateneo de Manila University

Square-shaped glass tubing, blow torch, ink and matches

Objective

Demonstrate the convection of heat in a liquid.

Description of the Set-Up

The set-up consists of a close square-shaped glass tubing with an opening at the top for adding ink or dye, a blow torch, water, ink or dye, dropper, matches, iron stand and clamp.

Demonstration

Mount the glass tubing on the support as shown in the illustration. Fill the tube with water. Using the dropper, put ink or dye in the water. Light the blow torch and heat the lower-left part of the vertical arm of the glass.

Describe the motion of the fluid. What is the direction of the current?

What happens to the fluid when the lower-right part of the vertical arm of the glass is heated?

Precaution

Put any combustible material away from the lighted blowtorch.

The mounted glass tubing is heated at its lower-right portion. To which direction will the current flow? Why?

The mounted glass tubing is heated at its lower-right portion by a blow torch

Interactive Lecture Demonstration: Convection current in air

by Erees Queen Macabebe and Ivan Culaba
Department of Physics, Ateneo de Manila University

Candle, mosquito coil, matches, and a transparent box with two chimneys

Objective

Demonstrate convection of heat in air.

Description of the Set-Up

The set-up consists of a transparent box with two chimneys, a candle and a mosquito coil. The match is used to light the candle.

Demonstration

Light the candle and place it inside the box near the opening of one of the chimneys. Light the mosquito coil until it glows red then put off the flame. With the box closed, place the mosquito coil near the top of the second chimney.

Observe what happens to the smoke coming from the coil.

The lighted mosquito coil is placed near the opening of the second chimney.  Where did the smoke from the mosquito coil go? Why?

A lighted mosquito coil about to be placed on top of the chimney that has no candle

A lighted mosquito coil placed on top of the chimney that has no candle