Q&A - PSLE Science

[chrisu]

For Q21, the correct answer is (2). S1 and S3 closed. Though S1 is the only switch needed to be closed for bell to work, S3 can be closed as given by the answers even it is not required.


Once S2 is closed, the bell will not ring.

P5G:

Please help.

http://www.orlesson.org/orp/10Sc/2010-P6-Sc-SA2-Nanyang.pdf


Question 18 - Energy
Worksheet answer is (1). Should the correct answer be (2)?


Question 21 - Electricity
Worksheet answer is (1). Should the correct answer be (2)?


TIA.

[Nebbermind]

atutor2001:

IMTRYINGSTUFF:

Maybe the force of gravity and the magnetic force of attraction are the same in this toy and so they cancel seach other out and the sphere remains floating in the air, like if you put a sphere in space and not move it.

That is the ideal equilibrium which cannot happen in real life because of

1) air around the sphere (frictional force)
2) uneven distribution of the mass of the sphere with the magnet in it
3) the magnetic force is not a single \"point\" force but a distribution of many forces..in many directions..
...

It is not good to mislead young children. I still remember once a cute little guy in this forum asked : Can penguins' fly? - because he saw a BBC youtube vido showing penguins flying.

this magnet qn wld probably makes sense if the magnet in the toy is placed at the bottom rather than top.

then using the principle of unlike poles, the ball will float (but I think still need to be held vertically in place by a cylinder).

[tianzhu]

Hi Hifive


Good Morning.

Your question reminds one of the “floating clip” questions.

Please refer to Primary 3 Science (2011): Magnets, Free response Q4.
http://www.oldschool.com.sg

This is a popular question in primary science; it’s about a floating metal clip.
Notice that a string is tied to one end of the clip, the other end of the string is connected to the ground. In this case, the magnet attracts the clip, but the string prevents the clip from being pulled to the magnet.

However, in your question, the sphere is floating, but is not attached to a string. It’s interesting to know what went through the mind of the question setter when he crafted the question. How does the sphere float?

I remember seeing one PSLE science question on “Maglev train”. This is a special train that floats several centimetres about the track while moving. This touches on magnetic levitation.

Do not be to too overly concern with the term \"levitation”. I think you cannot find it in your science textbook. Just view it as a method by which an object is suspended with no supports other than magnetic fields.

I think you can find floating pen and globe in the market. Some interesting sites,

http://www.vat19.com/dvds/stellanova-levitating-globe.cfm
http://www.levitationfun.com/globe.html

I think you need to have another set of magnet at the base of the stand for the set up in your question to work.Please check the answer with your science teacher.

Best wishes

[Hifive]

Hi tianzhu


Thanks for your explanation and the link you provided for further understanding. Will let my DS study it and ask him to check with his teacher.

[atutor2001]

The truth is (if my memory didn’t failed me), I have seen such a toy before. However, the concept behind its operation is not so simple as that required by the question. There are more complex features inside the sphere.


The sphere probably need to have a central metal core (made of magnetic material) and with many small magnets pasted "evenly" on the inner surface of the sphere (with their like poles as the magnet of the "stand" facing outwards).

[P5G]

Please help.


http://www.orlesson.org/orp/10Sc/2010-P6-Sc-SA2-Nanyang.pdf


Question 1 - Populations of organsims
Worksheet answer is (2). Please advise how to get A and D only.


Question 18 - Energy
Worksheet answer is (1). Should the correct answer be (2)?


Question 21 - Electricity
Worksheet answer is (1). Should the correct answer be (2)?


TIA.

[tianzhu]

Hi P5G


Question 1 - Populations of organsims

Based on the context in the question, one can see (B) and (C) are obviously offside.

Given the four options, only option (2) remains.

(A) is logical; from the end of week 1 to beginning of week 2, the population of x stays constant. Hence, birth rate equals to death rate is a logical explanation.

(D) is logical, from the graph; one can see that when Y increases, X decreases.

I’d go for option (2).

Best wishes

[P5G]

Please help.


http://www.orlesson.org/orp/10Sc/2010-P6-Sc-SA2-StNic.pdf

Q4 - Life cycles of a cat and a frog


Q14 - Water pollution


Q30 - Energy
Worksheet answer is (2). Should the correct answer be (3)?


TIA.

[tianzhu]

P5G:

Question 18 - Energy
Worksheet answer is (1). Should the correct answer be (2)?

Hi

The parallel rays of sunlight converge at a tiny spot through the magnifying glass. This raises the temperature of the paper till it catches fire.

Your answer of (2) is correct.

Best wishes

[tianzhu]

P5G:

Q4 - Life cycles of a cat and a frog

Hi

For Q4, the first issue to contend with is how to classify the life cycle of a cat. Is it 2-stage or 3-stage life cycle?

From PSLE Science Guide (MC), students learned that a cow has a 2-stage life cycle. Similarly, if you apply the same reasoning, a cat should also have a 2-stage life cycle.

However, some books may count the egg stage where the young animal is still inside its mother body, then there will be 3 stages.

From the context of the question, the setter appears to classify the cat as having 3-stage life cycle.

Given the four options in the MCQ question, students know that (B) and (D) are offside. So, the appropriate choice is option (3).

Best wishes