Question

40 (a) state what boiling means.

an engineer wanted to test if an electric pot can be used on a table with a thick glass top. he heated water in the pot for one hour.

(b) (i) explain why part a of the glass top was hotter than part b.

(ii) the glass top cracked after some time. explain why.

Explanation:

Define boiling

Boiling is the process where a liquid gains heat and changes state into a gas at a fixed temperature called its boiling point.

Explain temperature difference between part A and part B

Part A is directly under and in contact with the hot electric pot, so it gains heat from the pot by conduction. Part B is further away and does not receive heat directly from the pot.

Explain why the glass top cracked

Glass is a poor conductor of heat. When heated, part A gains heat and expands rapidly, while part B remains cool and does not expand, resulting in uneven expansion that causes the glass to crack.

Answer:

Question (a)

Boiling is the process in which a liquid gains heat and changes into a gas at a fixed temperature (its boiling point).

Question (b)(i)

Part A is in direct contact with the hot electric pot and gains heat from it by conduction, whereas Part B is further away and does not gain heat directly from the pot.

Question (b)(ii)

Glass is a poor conductor of heat. Part A gains heat and expands faster than Part B, and this uneven expansion creates internal stress that causes the glass top to crack.