Q&A - PSLE Science

[pixiedust]

http://i1197.photobucket.com/albums/aa424/pixie_dust8/sciq.jpg\">


Any comments about the above from MC Science PSLE Revision Guide ?

[Sun_2010]

pixiedust:

http://i1197.photobucket.com/albums/aa424/pixie_dust8/sciq.jpg\">


Any comments about the above from MC Science PSLE Revision Guide ?

Electricity is the term used for electric current. And current flows from the positive to negative. It is one of the conventions set before the structure of atom was discovered, so it was Benjamin Franklin set that the positive charge flows.
And this convention remained even though it was firmly established that it is the electrons that flow not protons.

http://en.wikipedia.org/wiki/Electric_current
this can be googled on many educational sites too

I am surprised by this highlighted point in MC PSLE revision guide.

Am I really getting obsolete

Calling experts !! :?:
tianzhu can you hear...

We need to have this sorted out, please

[Nebbermind]

Has always been the convention for current to flow from the higher potential to lower potential…u mean it has changed??

[tianzhu]

Hi Sun_2010


Paiseh, I am not an expert, just a “victim of circumstances”.

pixiedust,

I think you are looking at conventional current flow as compared to electron flow.

If are keen to find out more,please refer to these sites.

http://www.mi.mun.ca/users/cchaulk/eltk1100/ivse/ivse.htm
http://www.rare-earth-magnets.com/t-conventional-vs-electron-flow.aspx

Please check with the school teacher if this in the current syllabus.

There is also a short introduction on conventional/electron flow in Unit 17 Physics Matter (secondary school textbook) .

Best wishes

[pixiedust]

Thanks all.


I read the links on conventional current flow and electron flow. Now it is clearer.

My understanding is that for academic purposes ie. exams, the conventional flow will be adopted. As for the point in the MC guide : I would read it as conventional flow since the chapter did not cover electron. Hence, I will treat that point as incorrect.

[smartmummy]

Verysuperkiasu:

smartmummy:

i have a qn.

Is it correct to say that the stress ball can be compressed?Explain ur answer.

pls help me answer the qn.thank you.

Hmmm... it's quite tricky. Stress ball is a solid and we know solids can't be compressed as it has a definite shape and definite volume. But the fact that it can be squeezed into a smaller size it's because of the air spaces inside it (just like a sponge). So, yeah it's a good question, can we use the word 'compress' in this case???

Answer gave like as follows in the Assessment book Science Process Skills P3/4,

Yes,the stress ball is in the solid state.There are tiny air spaces inside the foam rubber which can be compressed when the ball is squeezed.As soon as the hand squeezing it is removed,the stress ball is able to return to its original shape and size.

[Verysuperkiasu]

[/quote]


Answer gave like as follows in the Assessment book Science Process Skills P3/4,

Yes,the stress ball is in the solid state.There are tiny air spaces inside the foam rubber which can be compressed when the ball is squeezed.As soon as the hand squeezing it is removed,the stress ball is able to return to its original shape and size.[/quote]



Thanks for answer. So…we can still the word ‘compress’ for the stress ball? Coz it kind of contradicts the property of solid - can’t be compressed.

[Tang]

simple88:

Hi,


Nanyang 2010 SA2 P4 Q23
Kharil conducted an experiment to find out how the colour of a material affects the amount of heat absorbed by the cloth. He placed two similar blocks of ice in the basketball court and covered them with cloths of different colours. Cloth A is pink and cloth B is dark red.

Which one of the following statements is a likely hypothesis for the experiment?
1) The block of ice covered by cloth B will melt first.
2) The block of ice will melt because of heat from the sun.
3) Both blocks of ice will absorb heat from the surroundings.
4) Cloth B will release more coldness to the surroundings.

The answer key is (3) but I thought should be (1).
The definition of Hypothesis I gathered from Science PSLE Guide Book is what you predict the results of an experiment will be.

Can someone help to enlighten me? Thanks!

Hi,
The answer is in the AIM.
So (1) is correct.

[tianzhu]

Verysuperkiasu:

So....we can still the word 'compress' for the stress ball? Coz it kind of contradicts the property of solid - can't be compressed.

Hi

You’ve brought up a good point, the word 'compress' for the stress ball may be inappropriate.

We are given the understanding from smartmummy’s post that this question if from a P3/P4 assessment book.

I am not sure if smartmummy has summarised the question from the book. If she did, the question may not appear as it is in its original form.

I think many P3 students are not familiar with stress ball, as such I believe there should be a picture or image of a stress ball together with a brief description of the material used to make the ball in the question.

A point to note is that the answer stresses those tiny air spaces inside the foam rubber can be compressed when the ball is squeezed.It’s the air spaces which can be compressed not the stress ball.

It’ll be helpful if smartmummy could post the original question, if possible. Perhaps, the term squeeze may be more suitable.

The concept on why \"sponge is a solid\" is applicable to this question.

Best wishes

[adhdadhd]

Compress is related to state of Material, eg: for air, it can be compressed to become liquid, another state of material. since sponge ball is not material, so is not appropriate.