Q&A - PSLE Science

[tianzhu]

Thank you for your help.


Q31
http://www.wendykoh.com/08/primary5-rgssa2-science.pdf

At first look, I wanted to attempt this question using the concepts of different characteristics of material. However, the answer sheet suggested that this question is from the topic cells.It goes along the line that the plastic bag gives a shape to the paper bag.I am still trying to understand the solution.

http://farm4.static.flickr.com/3653/3448952874_2de045a4ee_o.jpg\">
http://farm4.static.flickr.com/3337/3448138349_214c5e744a_o.jpg\">

[tianzhu]

[quote]I am absolutely sorry for leading you on the wrong path ...my thoughts were somewhat distorted then !!!.[/quote]
Hi Dharma,
I appreciate your responses to my questions. Your answers came across as sincere, insightful and penetrating. One can feel the passion of a caring father who is concerned about the progress of his child. I know that much effort had been put in.
We may not arrive at the perfect answers, but through the exchanges of ideas and thoughts, one can pick up some useful tips. Even if we do make mistake, we make it with good intention.
Kids,particularly those without tuition, will definitely gain from your active participation. It’ll certainly inspire me to search for more questions.

[ksmama]

Hi, I think the paper bag question is both a test of materials and structure of a cell.

a) Set up A consists of a paper bag. Paper is thin and and not strong. It is thus unable to withstand the increase in pressure when air is pump into it and ends up bursting. On the other hand in set B, the paper bag is placed in a plastic bag. Plastic is a strong material and is able to support and protect the paper bag inside it. When air is pumped into this bag, the increased pressure inside the paper bag, the bag is cushioned and supported by the plastic bag outside it and therefore, it does not burst.

b) the animal cell has only a thin cell membrane as its covering. It is not strong and is not able to withstand the increase in pressure when water is pumped into it and ends up bursting. The plant cell, on the other hand, has an inner cell membrane, supported by an outer rigid cell wall. When water is pumped into the plant cell, the cell wall will protect and support the cell when its inner pressure increases and thus prevents it from bursting

[tianzhu]

Thank you for your help.

http://www.wendykoh.com/08/primary6-nanyangca1-science.pdf
The answer(ws) to the last part of the question is Potential energy --> Electrical Energy.Please help to explain why.
http://farm4.static.flickr.com/3408/3449160885_4227ce975c_o.jpg\">
http://farm4.static.flickr.com/3318/3449160899_a9bf5c4f6d_o.jpg\">

[Dharmaratnam]

ksmama:

Hi, I think the paper bag question is both a test of materials and structure of a cell.

a) Set up A consists of a paper bag. Paper is thin and and not strong. It is thus unable to withstand the increase in pressure when air is pump into it and ends up bursting. On the other hand in set B, the paper bag is placed in a plastic bag. Plastic is a strong material and is able to support and protect the paper bag inside it. When air is pumped into this bag, the increased pressure inside the paper bag, the bag is cushioned and supported by the plastic bag outside it and therefore, it does not burst.

b) the animal cell has only a thin cell membrane as its covering. It is not strong and is not able to withstand the increase in pressure when water is pumped into it and ends up bursting. The plant cell, on the other hand, has an inner cell membrane, supported by an outer rigid cell wall. When water is pumped into the plant cell, the cell wall will protect and support the cell when its inner pressure increases and thus prevents it from bursting

Dear ksmama,

You certainly have given a very clear explanation. Thanks.

Tianzhu, somehow I was not sure of what the question was trying to say about the paper bags. The 1st sentence talked about 2 paper bags. The 2nd sentence mentioned that there was a thick plastic bag that was the same size and shape of the paper bag.

The picture however, shows a plastic bag and another with paper bag inside the plastic bag.

I was also confused ........

[Dharmaratnam]

tianzhu:

Thank you for your help.

http://www.wendykoh.com/08/primary6-nanyangca1-science.pdf
The answer(ws) to the last part of the question is Potential energy --> Electrical Energy.Please help to explain why.
http://farm4.static.flickr.com/3408/3449160885_4227ce975c_o.jpg\">
http://farm4.static.flickr.com/3318/3449160899_a9bf5c4f6d_o.jpg\">

The answers for part (c) and (d). I don't think that the ws answer is correct.

# Chemical potential energy is converted to electrical energy which will be converted to light, sound and heat energy when switches A,B,C, and A,B,C and D are closed.

[tianzhu]

Dharmaratnam:

The answers for part (c) and (d). I don't think that the ws answer is correct.
# Chemical potential energy is converted to electrical energy which will be converted to light, sound and heat energy when switches A,B,C, and A,B,C and D are closed.

Hi Dharma

How about thinking along this line?
The circuits are in parallel, meaning the amount of current flowing through each part is not the same.

The branch in switch D has no bulb, buzzer or nichrome wire, hence it has the lowest resistance.Therefore, more current flows through it.This also means the bulb, buzzer and nichrome wire are now receiving less current than previously.Less current means less power, therefore they cannot function.

In this way, the only energy chain is Potential to Electrical.

Going through my son's textbook, I observed that series and parallel circuits are not covered extensively.There are some information on batteries in series and parallel.But they are taught that the bulb shines less brightly when there is less current through them.Perhaps this question is crafted to stretch their young minds a little more.

[ksmama]

Hi , my battery answer would go with Dharmaratnam’s.

Assuming the examiner is not being difficult by requiring the kids to consider if the batteries are old or new batteries, the current from the batteries are split into 4 pathways, resulting in the conversion of chemical potential to electrical to sound annd heat energy. However, for our own discussion purpose, should the batteries be near their end- of- life… yes, the conversion may be just chemical to electrical or perhaps some wasted heat energy.
Actually for part A, to be more accurate, the conversion should be chemical potential energy to heat energy and light energy in the bulb.

[ksmama]

Sorry , type faster than I think.

Part A, I mean more accurate to be Chemical potential e to electrical to heat and light e
part c and d as Dharmaratnam’s( I missed out light e)
weak batteries=> chemical pot e to electrical to

[Dharmaratnam]

Dharmaratnam:

tianzhu:

Thank you for your help.

http://www.wendykoh.com/08/primary6-nanyangca1-science.pdf
The answer(ws) to the last part of the question is Potential energy --> Electrical Energy.Please help to explain why.
http://farm4.static.flickr.com/3408/3449160885_4227ce975c_o.jpg\">
http://farm4.static.flickr.com/3318/3449160899_a9bf5c4f6d_o.jpg\">

The answers for part (c) and (d). I don't think that the ws answer is correct.

# Chemical potential energy is converted to electrical energy which will be converted to light, sound and heat energy when switches A,B,C, and A,B,C and D are closed.

Hi Tianzhu,

In a parallel circuit, the electric current can flow along several paths. The amount of electric current along each path will be same. If we replace the buzzer and nichrome wire with similar bulbs as the one in the circuit, each of the bulbs will light up as bright as the first one and brightness of the bulbs remains the same even if new paths with bulbs are added.

Therefore, coming back to the qn, when switches A,B,C,and D are closed, the bulb will light up as brightly as before, the buzzer will sound as loud as before and the nichrome wire will glow the same as before.

I still think that potential changes to electrical energy to light + sound + heat.

# Pls do not look into it too deeply....resistance is NOT taught in P5/P6..so don't worry too much about it.

So, even if switch D is closed, electric current will still flow through all 4 loops ...therefore answers to (c) and (d) are the same. Think the examiner just trying to test the basic understanding of the child with regards to parallel circuits in this case.