Answer:
When a blade of cold knife is touched to hot glass chimney there is a sudden drop of temperature on the spot where the blade touches. As a result it cracks.
Explanation:
When a blade of cold knife is touched to hot glass chimney there is a sudden drop of temperature on the spot where the blade touches. This decrease in temperature makes the glass to contract. The stress developed on the site of contraction is responsible for the cracking of the glass chimney.
