Q&A - PSLE Science

[chrisu]

yes, it's possible and the handle shadow cannot be seen. Just position the handle behind. Of course need to tilt a bit only.

Nebbermind:

For E, have u tried positioning the handle such that it will not cast any shadow?

[Nebbermind]

chrisu:

yes, it's possible and the handle shadow cannot be seen. Just position the handle behind. Of course need to tilt a bit only.

Nebbermind:

For E, have u tried positioning the handle such that it will not cast any shadow?

when tilted only a bit, the shadow is more like D. I can't get anything near E as the handle's shadow will appear. anything, just for discussion only, not fault finding.

[atutor2001]

Hi Chrisu


Thank you for producing shadow D. It is my mistake to assume that the light source is along the central-line of the cup, which will then produce symmetrical curves. You are the best parent any child can find.

[pixiedust]

Yes, thank you Chrisu! You are the BEST :rahrah:

Thank you for being persistent with this.

I re-tested with help from my dh - the non-sharp edges are due to the 'diffused' light source from the torch. We remove the glass covering so there is a single light source.

Here are our shadows :
http://i1197.photobucket.com/albums/aa424/pixie_dust8/image_c.jpg\">
http://i1197.photobucket.com/albums/aa424/pixie_dust8/imagee.jpg\">

Conclusion: Agree with you shadows B,C,D,E can be formed.
With input from Tang, answer for Q20 should be (4) but it is still incorrect as E is not included.

[smartmummy]

http://i55.tinypic.com/20hrsao.jpg\">


Hi All!
I am so sorry to disturb u all.The original qn I posted here.
I confused,for the sponge they said the air escaped when we squeezed,but here they said air compressed when we squeezed.

[vlim]

Just now my ds was doing this qn... In an enclosed aluminum box with a light bulb on. They want to test with what inner wall Colour, the temperature will be the highest with the bulb on for 15 Min. The answer is black follow by grey then white... But my ds answer to it is exactly opp as he said tt black absorb heat and conducted away fast thru the aln box while white reflect light within box so make the temp high ... So I was confuse ... :?

So can someone pls enlighten me :please: :please:

[cimman]

atutor2001:

E is not acceptable because it is too elongated. Proportion-wise, the shadow cannot be so long.


Conclusion : none of the options is correct.

yeah, actually in a number of science questions, the answers are theoretical. In practice, none of the options are correct.

[tianzhu]

vlim:

Just now my ds was doing this qn... In an enclosed aluminum box with a light bulb on. They want to test with what inner wall Colour, the temperature will be the highest with the bulb on for 15 Min. The answer is black follow by grey then white... But my ds answer to it is exactly opp as he said tt black absorb heat and conducted away fast thru the aln box while white reflect light within box so make the temp high ... So I was confuse ... :?

So can someone pls enlighten me :please: :please:

Hi

This question is pretty similar to one from PSLE 2009, remember the one with a toy, white and black coloured vanes and Ahmad shining a torch.

More light energy from the light bulb is absorbed by the black inner wall than the light coloured ones. The absorbed light energy is then transformed to heat energy. As the black inner wall absorbs the most light energy,there is more light energy being changed into heat energy,it becomes hotter than the rest.

Why do mothers tell their kids to wear light coloured clothes when they are out in the sun?

This link helps.
http://www.sciencekids.co.nz/experiments/lightcolorheat.html

Best wishes

PS --- Students should note that conduction of heat takes place when two objects are touching one another. (PSLE Science Guide, MC)

[tianzhu]

smartmummy:

I am so sorry to disturb u all.The original qn I posted here.
I confused,for the sponge they said the air escaped when we squeezed,but here they said air compressed when we squeezed.

Hi

Thank you for posting the question.

On the highlighted portion,are you referring to answers given on 2 different questions?

Best wishes

[chrisu]

Thank you atutor2001 and pixiedust. Yes pixiedust, the source (torch) is important to produce a sharp shadow.


Hi Nebbermind,
The difference between shadow D and E is D I achieved by shining from bottom to up while E is achieved by shining from top to botttom.

Here is one with the handle hidden behind for shadow E;
http://img.photobucket.com/albums/v160/guppiesonli/Misc/Shadow-E-2.jpg\">

Pls note that the torch position and the camera position is different. So pls do not be mistaken by the photos that I'm shining directly at the mug.

Cheeers