Q&A - PSLE Science

[tianzhu]

ms_lim:

Hi, can you help to explain this question? Ans key is 1 but my dd's ans is 4 :

Hi

The WS’s answer is correct.

In primary science, students learned that adding batteries in series (up to a certain point) increase the brightness of a bulb.

There is no way we can tell whether the bulb in circuit P would last longer than the bulbs in circuit Q. It may or may not be.

Let’s take an example; if you buy a new bulb for your house, sometimes this new bulb may fail first when compared to the older bulbs in the house. Of course, it may also last longer.

Best wishes

[tianzhu]

ms_lim:

Ans key for :
bi) It would move towards the flask with black surface.
ii) Black surface absorbs heat faster, thus causing the mouth of the flask to expand faster. The coloured ink will then move towards the expanded part of the tube.
My dd's answer :
bi) It would move towards the flask with white surface.
ii) Black surface absorbs heat faster, so the gas inside the black surface flask will gain heat faster and expand. As gas expands more than solid, the ink will move towards the flask with white surface.

Hi

The key point to consider is \"after a while\".We can have different opinion on how long is \"after a while\".

The flask will expand first before the air inside it as heat reaches the flask first.

The first observation is the ink moving towards the flask with the black surface.

Best wishes

[atutor2001]

ms_lim:

Hi, can you help to explain this question? Ans key is 1 but my dd's ans is 4 :

http://i51.tinypic.com/2hf2gr9.jpg\">

Sorry Deleted because read options wrongly.

A & B are correct.

[atutor2001]

ms_lim:

Please help to explain this qn :

http://i52.tinypic.com/8yru38.jpg\">
Ans key for :
bi) It would move towards the flask with black surface.
ii) Black surface absorbs heat faster, thus causing the mouth of the flask to expand faster. The coloured ink will then move towards the expanded part of the tube.
My dd's answer :
bi) It would move towards the flask with white surface.
ii) Black surface absorbs heat faster, so the gas inside the black surface flask will gain heat faster and expand. As gas expands more than solid, the ink will move towards the flask with white surface.

My recommendation is :

The ink drop will first move towards the flask with the black surface, After that it will move towards the flask with the white surface.

Black absorbs heat faster than white causing the black surface flask to expand more than the white surface flask. As a result, the ink drop moves towards the black surface flask first. After that, the air in the black surface gets heated up and expands faster than the air in the white surface flask, forcing the ink drop to move in the opposite direction, towards the white surface flask.

[andante]

Hi all,

My dd has done edgefield science paper and there are discrepancies between the answer keys and her answers. Can someone help ?

Q11 (3) but answer key is (4)
Q12 (4) but answer key is (2)
Q13 (2) but answer key is (1)
Q14 (2) but answer key is (1)
Q16 (3) but answer key is (2)

Thanks.

[bcs-dad]

Hi All,


For the following question, I thought the answer should be 1) A only. My DS also think the same way. But the answer key says the right answer is 2) A and D

http://i56.tinypic.com/2pqn7dk.png\">

For setup D, I thought there is not way for the water to evaporate from second tube while some water can be evaporated from the first one. But for setup A, the the amout to water that can be evaporated can be same..

Can some body help me why 2) is correct than 1) ??

[ms_lim]

tianzhu:

ms_lim:

Hi, can you help to explain this question? Ans key is 1 but my dd's ans is 4 :

Hi

The WS’s answer is correct.

In primary science, students learned that adding batteries in series (up to a certain point) increase the brightness of a bulb.

There is no way we can tell whether the bulb in circuit P would last longer than the bulbs in circuit Q. It may or may not be.

Let’s take an example; if you buy a new bulb for your house, sometimes this new bulb may fail first when compared to the older bulbs in the house. Of course, it may also last longer.

Best wishes

Dear tianzhu and atutor2001,
Thanks for the explanation. My dd and me misunderstood option C. Now we understand.

[ms_lim]

atutor2001:

ms_lim:

Please help to explain this qn :

http://i52.tinypic.com/8yru38.jpg\">
Ans key for :
bi) It would move towards the flask with black surface.
ii) Black surface absorbs heat faster, thus causing the mouth of the flask to expand faster. The coloured ink will then move towards the expanded part of the tube.
My dd's answer :
bi) It would move towards the flask with white surface.
ii) Black surface absorbs heat faster, so the gas inside the black surface flask will gain heat faster and expand. As gas expands more than solid, the ink will move towards the flask with white surface.

My recommendation is :

The ink drop will first move towards the flask with the black surface, After that it will move towards the flask with the white surface.

Black absorbs heat faster than white causing the black surface flask to expand more than the white surface flask. As a result, the ink drop moves towards the black surface flask first. After that, the air in the black surface gets heated up and expands faster than the air in the white surface flask, forcing the ink drop to move in the opposite direction, towards the white surface flask.

Thanks atutor2001 and tianzhu for the recommended answer.

[tianzhu]

bcs-dad:

For setup D, I thought there is not way for the water to evaporate from second tube while some water can be evaporated from the first one. But for setup A, the the amout to water that can be evaporated can be same..

Can some body help me why 2) is correct than 1) ??

Hi

The experiment set up is to find out if plants take in water.

The cover in set A and the oil in set up D serve to prevent the water from evaporating. This helps to confirm that the decrease in water level in the container with the plant is due only to water absorbed by the plant’s roots.

Hence, you may use set A or set up D.

Best wishes

[atutor2001]

bcs-dad:

Hi All,


For the following question, I thought the answer should be 1) A only. My DS also think the same way. But the answer key says the right answer is 2) A and D

http://i56.tinypic.com/2pqn7dk.png\">

For setup D, I thought there is not way for the water to evaporate from second tube while some water can be evaporated from the first one. But for setup A, the the amout to water that can be evaporated can be same..

Can some body help me why 2) is correct than 1) ??

I share the same answer as you.

My reasoning is as follows :
For any experiment conducted, we must ensure that it is a fair test (implicitly \"understooded\")
For a fair test, only 1 variable can be changed.
For D, there are 2 variables that have been changed. (therefore not fair test)
(in experiment, we cannot allow any possible source of error and the easiest way is to stick closely to the requirement that only 1 variable is changed)