Q&A - PSLE Science

[atutor2001]

Herbie:

i hv a qn.


Raju wante to find whether a nail was magnetised. He put it near a magnet, a compass and a paper clip. He recorded his observations below

A. It repelled the magnet.
B. It attracted the magnet.
C. It attracted the paper clip.
D. It could move the compass needle.

From which of the above observations can be sure that the nail waagnetised?

1. A only
2. A and C only
3. B and C only
4. A, B, C and D

Answer is (1) A only because magnet can only be confirmed by repulsion. Attraction can happen between a magnet and a magnetic material.

[Herbie]

hi atutor,

The answer on the answer sheet is 3.

If the nail is being magetised, it shld also be able to attract the paper clip and attract the magnet too right??

[atutor2001]

Herbie:

hi atutor,

The answer on the answer sheet is 3.

If the nail is being magetised, it shld also be able to attract the paper clip and attract the magnet too right??

I have to disagree with the answer given in the answer sheet.

The key word in the question is \"can be sure\". That means the option chosen must be 100% correct with no allowance for other possibility.

It is true that if the nail is being magnetised, it should be able to attract the paper clip and the magnet.

However,

Possibility 1
It is also true that if the nail is NOT magnetised, it would still be attracted to the magnet.

Possibility 2
It is also true that if the nail is NOT magnetised but if the paper clip is magnetised, the nail will be attracted to the paper clip. (unless it is stated clearly in the question that the paper clip is not magnetised)

Therefore, it is a norm that to confirm whether if an object is a magnet, we need to use repulsion.

[Vanilla Cake]

P5G:

By the way, do you know the answers to Chong Fu 2011 CA2 Science.

Should the answer for 39 be
a). A and D instead of A and F.
c). Kinetic energy --> Kinetic energy + ??? (No idea) instead of Kinetic energy --> Heat energy + Sound energy.
Please help. TIA.

Hi P5G,

39(a)
No kinetic energy when the roller coaster was at the starting point and when it hits the bumper (finishing point). So, the positions are A and F.

When it is at the starting point, it has no kinetic energy but it has the most gravitional potential energy. So, the position should be A.

39(c)
When it hits the bumper at F, it will produce sound and heat due to the impact. So the energy conversion will be from kinetic energy to sound energy and heat energy.

Hope this helps.

[P5G]

Vanilla Cake:

P5G:

By the way, do you know the answers to Chong Fu 2011 CA2 Science.

Should the answer for 39 be
a). A and D instead of A and F.
c). Kinetic energy --> Kinetic energy + ??? (No idea) instead of Kinetic energy --> Heat energy + Sound energy.
Please help. TIA.

Hi P5G,

39(a)
No kinetic energy when the roller coaster was at the starting point and when it hits the bumper (finishing point). So, the positions are A and F.

When it is at the starting point, it has no kinetic energy but it has the most gravitional potential energy. So, the position should be A.

39(c)
When it hits the bumper at F, it will produce sound and heat due to the impact. So the energy conversion will be from kinetic energy to sound energy and heat energy.

Hope this helps.

Hi,

Noted. Thanks. I will just have to ignore those wordings below the boxes as they are so confusing.

[P5G]

Please help.


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Should the answer for (c) be:

Plot D. It has the least number of plants per plot so there is less competition for nutrients, water and space.


TIA.

[P5G]

Please help.


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Will I be marked wrong if my answer for (c) is

Both plants can carry out respiration.


TIA.

[P5G]

Please help for 33 (b)


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TIA.

[Verysuperkiasu]

atutor2001:

P5G:

Please help.


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TIA.

(a) The rate of photosynthesis of water plants without the presence of light (in darkness) is faster at higher temperature.
OR
The rate of photosynthesis of water plants without the presence of light (in darkness) is slower at higher temperature.
....

(b) All the water plants will die because there is no light for it to carry out photosynthesis to make food.

Sorry to ask - but the inner surface of the box is aluminium foil although outer is glass, so by right, there shouldn't be any photosynthesis that takes place since light can't penetrate? Pls correct me if I'm wrong.... thanks.

[atutor2001]

Verysuperkiasu:

atutor2001:

(a) The rate of photosynthesis of water plants without the presence of light (in darkness) is faster at higher temperature.
OR
The rate of photosynthesis of water plants without the presence of light (in darkness) is slower at higher temperature.
....

(b) All the water plants will die because there is no light for it to carry out photosynthesis to make food.

Sorry to ask - but the inner surface of the box is aluminium foil although outer is glass, so by right, there shouldn't be any photosynthesis that takes place since light can't penetrate? Pls correct me if I'm wrong.... thanks.

Yes you are right that photosynthesis cannot take place with the aluminium covering the box.

However, this question is testing the concept of \"hypothesis\" and not on photosynthesis. Hypothesis is a \"prediction\" on what we think is likely to happen for a certain situation. The information in our hypothesis needs not be factually correct. The purpose of creating an hypothesis is to help us in designing the experiment. We must then carry out an experiment to verify if our hypothesis/prediction is correct.

This question is actually reversing the order of activity. That is, we a given experiment set up and is asked to guess what is the likely hypothesis that the person is trying to verify/confirm.

From the experiment set up given, he has carried out the experiment in darkness. He has tried to collect air bubbles. He has changed the temperature (the variable that is changed).

From the above information, we can then guess that he is trying to find out how the rates of photosynthesis will be affected by temperature - which is how I come out with the hypothesis.

In other words, as long as the experiment set up can be used to verify the hypothesis that we have created our hypothesis should be accepted.


An example of a hypothesis that is not acceptable in this question is :

\"The lesser the amount of water is, the slower will be the rate of photosynthesis.\" (in the 2 set ups, the amount of water are the same and this experiment set up cannot be used to confirm the hypothesis)