r u saying: the ans in the ans key is "sheet Y gained more heat than X" ?

ur ans for (a) is correct.

why?

reasons:
1. both X & Y r similar sheets & of same material. This means both X & Y have the similar heat capacity, that means X & Y have the same ability to 'hold' similar amount of heat ;
2. the only difference is : Y is in contact with the heater. This close contact allows Y to gain " more heat per unit time " [note: Not more heat] than X. Thus, Y gains heat at a faster rate than X. [since more heat per unit time is higher rate of heat transfer]
3. Although Y gains heat from heater, Y also loses heat to X. So X gains heat at a slower rate as compared to Y. This also means Y insulates X from the heater.


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Thank u Snell.
Yes the ans sheet put the ans for (a) as
Sheet Y gained more heat and expanded more than X.
That is not quite correct right?

For (b) (i) n (ii) are the answers correct? (From ans sheet)

(i) the outer wall is further from hot tea hence it gained heat slower than inner wall

(ii) the inner wall gained more heat from the hot boiling water and expanded more than the outer wall, causing the cup to crack.

sorry for the late reply, there is no alert in this website to me.

the ans sheet is incorrect.

can u pls tell me what's the name of this assessment bk this qn comes from?

for (b)(i)

note that glass is an insulator of heat.

although ur written ans is correct, it is incomplete.

1. inner wall is in contact with hot tea

2. outer wall is in contact with the surrounding air at environment temperature.

3. glass is an poor conductor of heat. thus, it would take a long time for the heat from the hot tea to transfer via conduction from the inner wall to the outer wall.


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for (b)(ii)
ur written ans is incorrect.
there is no air in-between the glass thickness.

u already know that the inner wall is heated by the hot tea & the outer wall is at ambient temperature.

1. inner wall is heated by hot tea and hence expands.

2. glass is a poor conductor of heat, thus heat cannot transfer uniformly [note: the key word here is uniformly] through the thickness of the glass wall to the outer wall.

3. the outer wall is heated a little or not at all and it does not expand as much as the inner wall.

4. Therefore, there is non-uniform expansion within the thick glass wall that would result in the (glass) cup to crack. [Again, the key words here are the non-uniform or uneven expansion within the glass]


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Hi Snell. Thanks alot for your explanation (no.. u didnt reply late. I am appreciative that you took time to ans).
The qn is from 2018 CA1 P5 sci paper of CHIJ. The ans key given might be inaccurate.

thank you for ur reply!

if that is the ans key of CHIJ paper, then CHIJ setter is giving inappropriate ans.

I bought the papers set (qns n ans key) fr online source. I did check with the seller on the accuracies of the ans and he said those ans keys arent from teachers but from the correction done by pupils. He said only Sec or JC and above do they have ans keys provided by teachers. (Not sure if true).
So i cant rely 100% on these pri sch exam ans....