Q&A - PSLE Science

[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.
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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.

[ChiefKiasu]

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...

Sorry, Dharmaratnam, I have to say no again. The worksheet answer is actually very close to being correct.

When switch D is closed, we simply have a short circuit. Current going through a wire in parallel with other components will reduce the overall resistance of the entire parallel circuit to be lower than that of going through a pure wire. This means a huge amount of current goes through the wire, with very little current going through any of the other circuits in parallel with the short-circuited wire. None of the components will work, not bulb (light), nor the buzzer (sound), nor the nichrome wire (heat).

However, the batteries will be doing a lot more work due to the massive current they have to supply to the wire with very low resistance. This means that the chemical reactions in the battery will happen quicker, causing the batteries to heat up very quickly. For this reason, short circuits are known to cause batteries to explode!

So the correct answer should be:
Potential energy -> Electrical energy -> Heat energy in batteries

Here's a very easy to understand write-up:
http://www.furryelephant.com/content/electricity/complete-circuits/short-circuits/

[ksmama]

Hi ChiefKS, thanks for info. Discussed this with engineer friend as well and he explained to me the short circuit as well.


I guess the reason why the Science thread was not so active before, was that whereas in Maths we could work backwards to check the answer, it is more difficult to check on the answers to some Science questions. Sometimes paiseh if get it wrong... but I am glad that Tianzhu takes the trouble to scan the questions and post it on this thread so that people like me eg. can be stirred from slumber to read up on my kids' science references, to want to think through the questions and possible answers. I take this as a learning process: what I know, I can brush up; what I have forgotten, I am thankful to all the participating parents for the refresher course

Hopefully by next year, when its my kid's turn to take the PSLE, this rusty mind of my mind will be much clearer :lol:

[Dharma]

ChiefKiasu:

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...

Sorry, Dharmaratnam, I have to say no again. The worksheet answer is actually very close to being correct.

When switch D is closed, we simply have a short circuit. Current going through a wire in parallel with other components will reduce the overall resistance of the entire parallel circuit to be lower than that of going through a pure wire. This means a huge amount of current goes through the wire, with very little current going through any of the other circuits in parallel with the short-circuited wire. None of the components will work, not bulb (light), nor the buzzer (sound), nor the nichrome wire (heat).

However, the batteries will be doing a lot more work due to the massive current they have to supply to the wire with very low resistance. This means that the chemical reactions in the battery will happen quicker, causing the batteries to heat up very quickly. For this reason, short circuits are known to cause batteries to explode!

So the correct answer should be:
Potential energy -> Electrical energy -> Heat energy in batteries

Here's a very easy to understand write-up:
http://www.furryelephant.com/content/electricity/complete-circuits/short-circuits/

Good Morning Chief Kiasu,Tianzhu and Ksmama,

Thanks Chief Kiasu for your clear explanation. I guess the most important thing here is the sharing of knowledge, exchange of ideas and learning from each other.

[tianzhu]

Hi

Thank you for your active participation.

First, we have to accept the fact that we are parents, not trained educators. For varied reasons, we may be more involved in our children’ studies than others.

Our knowledge in Primary Science is gained through reading up from our kids’ books .We have to agree Science questions nowadays are so much different from our times. Many a times, I am floored by them.Primary Science is fascinating and challenging. Kids have to use the right concepts and apply them appropriately to answer the questions. And, these have to done in one or two lines. You have to be stingy with words, using the right key words and phrases. Given the class sizes of about 40 active kids, it’s not easy for a school teacher to reach out to them. Therefore, particularly for those without tuition, parental guidance is important.

Let’s take this thread as a learning platform where parents and students exchange their ideas freely and learn from one another. We may not always come up with the so called model answers, but may offer some tips where another can tap to expand the ideas further. Along the way, mistakes will be made, but at least, we know that they are made with good intentions. We just want our kids to grow to their fullest potentials.

[corneyAmber]

Totally agree with tianzhu.


Btw, some of the Science content today are concepts learnt only in secondary school in the past…eg. potential and kinetic energy was covered only in sec. I suppose with Internet age and alot of enrichment centres with holiday programmes where information is readily available, they are expected to read & know much more than in the past. No right or wrong but learning is now generally accelerated and many of my friends with P5/P6 kids always scream the lack of time to do anything else other than prepare for PSLE. Just an obervation only.

[Dharma]

tianzhu:

Hi

Thank you for your active participation.

First, we have to accept the fact that we are parents, not trained educators. For varied reasons, we may be more involved in our children’ studies than others.

Our knowledge in Primary Science is gained through reading up from our kids’ books .We have to agree Science questions nowadays are so much different from our times. Many a times, I am floored by them.Primary Science is fascinating and challenging. Kids have to use the right concepts and apply them appropriately to answer the questions. And, these have to done in one or two lines. You have to be stingy with words, using the right key words and phrases. Given the class sizes of about 40 active kids, it’s not easy for a school teacher to reach out to them. Therefore, particularly for those without tuition, parental guidance is important.

Let’s take this thread as a learning platform where parents and students exchange their ideas freely and learn from one another. We may not always come up with the so called model answers, but may offer some tips where another can tap to expand the ideas further. Along the way, mistakes will be made, but at least, we know that they are made with good intentions. We just want our kids to grow to their fullest potentials.

Tianzhu,

You couldn't have been more correct!!!

[ChiefKiasu]

tianzhu:

...First, we have to accept the fact that we are parents, not trained educators. For varied reasons, we may be more involved in our children’ studies than others...

While not all parents are trained as educators, I would trust a group of well-meaning and educated parents with the web resources at their fingertips more than a Primary school teacher who only wants to teach and test material from the school's text. Yes, we all make mistakes, but the web and this Forum is so open that our mistakes will be discovered and corrected by other parents who may happen to be more familiar with the topic. Our combined responses will not only produce the best answer, but also highlight the common pitfalls that our children will probably encounter (since we encountered them ourselves!).

For this reason, I'm thankful for Tianzhu's earnest and untiring postings of the key problems he encounter while going teaching his children, and for the participation of members such as Dharma/Dharmaratnam and ks2me who share their thoughts on the problems.

[tianzhu]

Thank you for your help.

Please click at link and refer to MCQ Q14 on pg9.
( http://www.wendykoh.com/08/primary6-methodistsa1-science.pdf )

The given answer is (2).
However, from i-science P4, pg 67, we learned that mudskippers can also breathe through their skins by keeping it damp.They can also breathe by holding water in their mouths and gill chambers.

Do you know of any list showing how animals breathe?Is this answer correct?