2017 PSLE Discussions and Strategies

[Yanchong]

My son’s answer is also 1.

[ShevW]

If cut out should be 3. Triangle

[Happy70]

According to my daughter (who had unfortunately also put down option 1):


It could never have been the circle, whether alone or with another shape. If the paper with the cut-out circle is transparent, there would never be a circle shape appearing on the screen in the first place. If the paper with the cut-out circle is not transparent, the circle can never be shone onto the screen because the light rays forming the circle would be blocked by one or both of the pieces of opaque paper containing the triangle or square cut outs in front.

If the paper containing the triangle cut-out is transparent, then there could never be a triangle appearing on the screen. So only light rays forming the shape of the square could be shone onto the screen. But there is no option for “square only”.

If the paper containing the square cut-out is transparent, then there can never be the shape of a square appearing on the screen. And in that case, the only light rays that can pass through would form the shape of a triangle. If the paper containing both the square and triangle cut-outs are opaque, then again only light rays forming the shape of the square would appear on the screen (because the light rays forming the shape of the triangle would be partially blocked by the paper containing the square cut-out.

Sorry if this sounds convoluted. This was my daughter’s explanation to me.

[Musings]

Happy70:

Picture sequence:

First: circle
Second: triangle
Third: square

So answer is square and circle ??

My son chose circle only[/quote]

My daughter now thinks she understands why some say that the answer is 3. She says she may have misread / misunderstood the question during the exam -- basically, she did not appreciate the fact that the shapes are cut-outs from pieces of paper. She says if the shapes are cut-outs, then she can understand why the answer would be triangle only.[/quote]

Here is DS explanation.

Yes the crux is that the shapes are all cut outs.

The beam of light shines right through the circle (1st sheet). Circle of light is larger than the triangle because the sheet with circle cut out is furthest from the screen. Therefore, the light which falls on the screen is the triangle shape. The square is transparent.

[janet88]

congrats P6s...you are done with primary school education :rahrah: it's time to let go and relax.

[Mannap1]

:rahrah: :imcool: :boogie:

janet88:

congrats P6s...you are done with primary school education :rahrah: it's time to let go and relax.

[lee_yl]

Duplicate

[janet88]

for the p6s taking HMT tomorrow, all the best to you. after that, you will be freed as a bird.

[lee_yl]

Musings:

Here is DS explanation.

Yes the crux is that the shapes are all cut outs.

The beam of light shines right through the circle (1st sheet). Circle of light is larger than the triangle because the sheet with circle cut out is furthest from the screen. Therefore, the light which falls on the screen is the triangle shape. The square is transparent.

https://s1.postimg.org/67qkqaey3j/58_CB6057-0347-4696-_B4_FA-_FC2_C21846_B23.jpg\">

https://s1.postimg.org/2vkma2udxr/4_AF1_FDF5-16_F4-4786-8_EDD-5_AC912_BAFF36.jpg\">

Since the square is transparent, we treat it as non existent.

In pic A, the triangle is called silhouette not shadow.

In pic B, we see the shadow of the cut out circle.

May I know what is the exact question?

[Yrsincere]

I don’t quite get the question too.

But my understanding is the further an object from screen (nearer to light source), the bigger shadow on screen.
The nearer an object to screen (further from light source), the smaller the shadow.