To imitate the process of ice crystal formation in a cloud.
The ‘Hands On Energy Discovery Centre’ in Hobart can arrange for this demonstration to be shown to interested school groups.
Chest freezer lined with black velvet.
Dry ice
Spotlight lamp ( eg. projector lamp)
Shine a lamp into the freezer. The sides of the freezer are lined with
black velvet to reduce reflection. This makes it easier to see the
water droplets and ice crystals.
Breathe several times (gently) into the cold freezer. You will
immediately see a cloud form.
Scrape a very small amount of dry ice above the freezer so the ice
crystals fall into the cloud.
You will immediately see ice crystals forming and growing in size as
they fall through the cloud.
As the invisible water vapour in your breath comes into contact with the cold air, it turns back into a liquid by forming ( condensing ) on tiny dust particles (which are already present in the air) The cloud you see is therefore made of tiny water droplets.
Hydro Tasmania uses silver iodide instead of dry ice when they seed clouds because it is a more effective way of producing ice crystals.
Created on ... July 09, 2003