Q&A - PSLE Science

[autolycus]

The answer must be A if the light is travelling in the direction PQR. (It must be D if the light is travelling in the direction RQP.)


For the first case:

Light passes through P, or it can’t even get to Q.

Light lands on Q.

The light is partly reflected and partly absorbed by Q, so a bright image is seen. Q is opaque.

However, if Q is opaque, you can’t tell anything about R because light never reaches R.

=====

If the light is travelling in the direction RQP then the reasoning is the other way round. I can’t tell where the light is coming from, from your question.

[anneshirleygilbert]

Thank you for your reply. Light is travelling from the left, i.e. toward PQR. However doesn’t P have to be opaque? If P isn’t opaque, there would be no image of the heart at all because light can pass through transparent/translucent material.

[autolycus]

anneshirleygilbert:

Thank you for your reply. Light is travelling from the left, i.e. toward PQR. However doesn't P have to be opaque? If P isn't opaque, there would be no image of the heart at all because light can pass through transparent/translucent material.

Hi!

If P is opaque, then light won't reach Q. You won't see an image on Q.
If P is transparent and Q is opaque, light passes through P, lands on Q, stops there with a bright image.
If P is transparent and Q is opaque, light stops on Q and we never get to find out what R is like.

PQR
PQR
PQR
-QR <---- a beam of light from the left goes through P and hits Q but not R
PQR
PQR
PQR

[atutor2001]

anneshirleygilbert:

Thank you for your reply. Light is travelling from the left, i.e. toward PQR. However doesn't P have to be opaque? If P isn't opaque, there would be no image of the heart at all because light can pass through transparent/translucent material.

I agree with you that P is opaque because \"a bright heart-shaped patch of light is seen on sheet Q\" shows that there is a heart-shape hole in P. If P is transparent, then the entire sheet Q would be illuminated.

Since both P & Q are opaque, there is no answer in the given options.

[anneshirleygilbert]

Thank you Atutor2001. Just got reply from DD’s science teacher that none of the answers would fit. She thinks there may be some facts missing in the question.


Thank you, too, Autolycus. Sorry, I didn’t mention that there was a heart-shaped hole on Cardboard P, allowing light to pass through it, thus casting a heart-shaped patch on it. Thanks all the same.

I’m new on this forum. Chanced to find it when scouting for some answers for my daughter. Have spent much time reading the past posts. This has been a fantastic find for me. Thanks to all of you who have contributed to it.

[atutor2001]

Hi anneshirleygilbert


Welcome, with this site your kid doesn't need tutor. :lol:

[autolycus]

I would have to point out that the words used in the question say ‘allows light to pass through’, ‘does not allow light to pass through’, and ‘not possible to tell’.


Therefore, my answer is indeed correct, because P must allow light to pass through, whether it is made of opaque material or not. The shape of the image is irrelevant.

[atutor2001]

autolycus:

I would have to point out that the words used in the question say 'allows light to pass through', 'does not allow light to pass through', and 'not possible to tell'.


Therefore, my answer is indeed correct, because P must allow light to pass through, whether it is made of opaque material or not. The shape of the image is irrelevant.

Hi autolycus

Language wise I agree with your reasoning.

However, the question is focused on the properties of the material.
\"Which one of the following describes correctly the properties of the materials which P, Q and R are made of?\"

For example, one of the properties of metal sheet is \"it will not allow light to pass through\". If we cut a hole in the sheet, the material is still metal and the property of the material will still be \"it will not allow light to pass through\".

If the question is \"Which one of the following describes correctly the properties of the sheets P, Q and R?\", I think your argument will be valid.

Regards

[anneshirleygilbert]

Hello out there,


Need some help on 2 questions on Heat for P5.

Q1
Sarah wrapped two identical pieces of paper tightly around two rods, X and Y, separately as shown in the diagram below.

(sorry, don’t know how to show diagram)

Sarah placed each rod an equal distance over a lighted candle, ONE at a time, for 5 seconds.
She noticed that the paper on X had scorched marks on it while the paper on Y had caught fire and was burnt.
Based on Sarah’s observations, which one of the following conclusions is/are correct?
A: X is a good conductor of heat.
B: Y is a poor conductor of heat.
X is able to retain heat better than Y.
1.\tA and B only
2.\tA and C only
3.\tB and C only
4.\tA, B and C
The answer given was (1), but I think it should be (4). X, being a good conductor of heat was able to retain heat better than Y. Y is a poor conductor but caught fire from candle flame. Am I right?

Q2

A piece of metal sheet has a circular hole in the middle.

When the entire piece of metal sheet was heated evenly in an oven at high temperature for ten minutes, which one of the following describes and explains correctly what would happen?
1. Observation : The size of the hole remains the same\t
Explanation: The entire metal sheet expanded equally throughout
2. Observation : The size of the hole increases\t
Explanation: The entire metal sheet expanded equally throughout
3. Observation : The size of the hole increases\t
Explanation : Only the area around the hole expanded
4. Observation : The size of the hole decreases\t
Explanation : Only the area around the hole expanded
1.\t1
2.\t2
3.\t3
4.\t4

The answer given is (2)
But I think the observation should be the size of the hole decrease because the entire metal sheet expanded equally throughout, spreading out even to the hole, thus making the hole smaller. The expansion should not be limited to the area around the hole as the metal sheet was heated evenly in an oven. Is my reasoning right?
Unfortunately, this combination is not an option in the given answers. Pls. help.

[tianzhu]

Hi


I’ll take Q1 first.

Under the topic on heat, students learned that:

Good conductors of heat are materials that allow heat to pass through them easily.

Poor conductors of heat are materials that do not allow heat to pass through them easily.

She noticed that the paper on X had scorched marks on it while the paper on Y had caught fire and was burnt.
This is because the heat is conducted away from the paper by the rod X and the paper never gets hot enough to burn.

You may imagine rod X to be metal and rod Y to be wood.

The given answer (1) is correct.

Best wishes