Q&A - PSLE Science

[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

[tianzhu]

P5G:

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

Hi

I have the answer as you --- (3).

Best wishes

[tianzhu]

P5G:

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

Hi

For Q21, the answer is (2).

First, watch this video
http://www.youtube.com/watch?v=jxMV0wagR8o&feature=related

If S2 is closed, the wire act as a bypass for the current flowing through the bell, thus it’s easier for the current to flow through wire connecting S2 than the bell. The bell will not ring.

This gives rise to a situation called “short circuit”. A short circuit occurs when the current bypass the light bulb or bell and pass through another path with little resistance.

I can’t find anything on short circuit in my old MC PSLE science guide. If you are interested to find out more, you may find a short write up in this book Physics Matter, Chapter 17.

Some interesting sites which may give you more information.

http://www.energyquest.ca.gov/projects/open-short-circuit.html
http://www.furryelephant.com/content/electricity/complete-circuits/short-circuits/

Hope this helps.

Best wishes

[tianzhu]

P5G:

Q14 - Water pollution

Hi

Since the study is on water pollution, one may infer that the difference between the number of fish in the beginning and the number of fish alive in the end shows the pollution level of the water. In this question, the greater the difference, the more polluted the water in the river.

(1) ---- We cannot say the water in the upstream is not polluted as the difference in number of fish between the start and end is 10.

(2) ---- cage W ---- 10(difference) and cage Z ---- 9(difference)
cage X ---- 8 and cage Y ---- 5
So we cannot conclude that downstream is as polluted as upstream.

(3) ---- The study does not suggest that water downstream is more polluted than water upstream. In fact, the water at downstream is less polluted as shown by the study.

How about (2)?

Cage x ---- 8 and cage Y ---- 5
Their differences are less than those at W and Z.This suggests that water at deeper parts is less polluted.

I’m inclined to go for (2).

Best wishes