Q&A - PSLE Science

[tianzhu]

Hi


In answering Q16, may I suggest you have a recap on the topic of heat by reading your textbook and the PSLE Science Guide (MC).

Good conductors of heat allow heat to travel through them easily. Materials which do not conduct heat well are known as poor conductors of heat.

The cloth wrapped around Material P is scorched.

This is because heat is conducted away quickly from the cloth by Material Q and the cloth never gets hot enough to burn.

Material P is a poor conductor of heat and Material Q is a good conductor of heat.Hence (4) is correct.

Best wishes

[tianzhu]

Hi


Q13 tests students on the concept of a fair test.

For an experiment to be a fair test, you should change only the variable you are testing. All the other variables should be kept the same. Only one variable should be changed at a time.

In this question, you are finding out whether the colour or the type of surface affects the amount of heat absorbed by an object.

Therefore the variables you should change one at a time are the colour and type of surface of an object. Everything else such as materials, sizes must be the same.

Hence (1) is the correct answer.

Best wishes

[tianzhu]

Hi


In primary science, students learnt that the brightness of a bulb in an electric circuit is dependent on the amount of current flowing through it. When more current flows through a bulb, the bulb will be brighter.When less current flows through a bulb, the bulb will be dimmer.

The brightness of a bulb in a circuit depends on the

1) arrangement of batteries.
2) number of batteries.
3) number of bulbs.

A section on bulbs connected in series is covered in the textbooks as well as PSLE Science Guide.

There is also a section on bulbs in parallel in the Good to Know section in PSLE Science Guide(MC).

I have the old editions of these two books. Please help to confirm if they are in the new textbooks.

When more bulbs are added to a series circuit, the individual bulb shines less brightly. This is because current flowing through each bulb is reduced.(from PSLE Science Guidebook)

Given the same voltage/number of batteries,when two similar bulbs are connected in parallel, it will glow more brightly than when connected in series.

Things get trickier here, how to explain to P5 kids? We need to introduce term like resistance of bulbs to better explain this happening.

When two bulbs are connected in parallel, the combined resistance of the bulbs is less than the individual resistance. Given the same voltage or number of batteries, the bulbs will glow more brightly as compared to two similar bulbs connected in series. This is because there will be more current passing through them.

Now let’s get back to Q10.

We understand that given the same voltage/number of batteries,bulbs connected in parallel glow more brightly than bulbs in series. We also know that when more bulbs are added to a series circuit, the individual bulb shines less brightly.

So we know that bulbs in circuit B will be the least bright. Therefore through elimination, we know that (2) and (3) are offside.

We observe that circuit D has more batteries connected in series than circuit C.

Therefore, the bulbs in circuit D will be brighter than circuit C.This is because there is more current flowing through the bulbs.

Hence, D,C,A, B is the correct sequence.

Best wishes.

[youngtay]

Mr Tianzhu


Thank for your help.

Best Wishes

[tianzhu]

youngtay:

Mr Tianzhu


Thank for your help.

Best Wishes

Hi youngtay

You're welcome.

Best wishes

[youngtay]

Please help.



http://www.orlesson.org/orp/09Sc/2009-Sc-SA2-Nanyang.pdf

question 22, the worksheet answer is 3, my dd's answer is 2, and for
question 29, the worksheet answer is 3, my dd's answer is 1, can help to confirm which is correct?

TIA

[tianzhu]

Hi youngtay


Good Morning

For Q22, your kid’s answer is correct. Option (3) shows three batteries connected in series, however one of them is in different direction.

I am more inclined to go for option (2).

For Q29, the WS’s answer is right.

Change A ----- The greater the number of bulbs, the dimmer they are. Thus, when one bulb is removed, bulb X glows brighter.

Change B ----- As more batteries are added in series, more current is available and the bulbs become brighter.

Change C ----- The batteries(2 sets of two batteries) are in parallel, therefore the brightness of bulbs remains the same as original set up.

Change D ----- Given the same voltage/number of batteries, when two similar bulbs are connected in parallel, it will glow more brightly than when connected in series.

Change A, B and D will result in having a brighter bulb X.
Option (3) is correct.

Best wishes

[WS1234567]

youngtay:

Please help.



http://www.orlesson.org/orp/09Sc/2009-Sc-SA2-Nanyang.pdf

question 22, the worksheet answer is 3, my dd's answer is 2, and for
question 29, the worksheet answer is 3, my dd's answer is 1, can help to confirm which is correct?

TIA

For Q22,
option 1 is wrong because the driection of the batteries are not the same.
option 2 is right. the change in the position of the switch did not change the actual setup.
option 3 is wrong because the two sets of batteries used to be in parallel but now they are in series.
option 4 is wrong because now the bulbs are placed in parallel and not in series.

I think the worksheet answer could have a typo error.

For Q 29,
Answer should be 3.
IN change C, notice that the poles of the batteries cancel each other out leaving the circuit to have the actual effectiveness of 2 batteries, ie. same as before.
All other changes did make the bulbs brighter.

[youngtay]

Mr Tianzhu and WS1234567


Tks for your help.

Best wishes

[kancheongmum]

naggo-nitemare:

Ler:

[quote=\"tianzhu\"]
Hi everyone. V paiseh for error.
Q15 - explanation should be \"Anther is shorter than stigma\" to prevent SELF pollination.

Tks

[/quote]Hi nago-nitemare
Q15) I have check with DS school science teacher ans should be option (4).
A- flower is beautiful means petals colourful and bright to attract insects
B- nectar sweet attract insects
C - this adaptation does not help
D - Stigma is hanging out of the flower this adaptation helps because insects may land there because of the nectar

for Q21, options (1) (2) and (3) I would say are all correct. Looking at circuit again, actually we just need to close S1 and it will already be a closed circuit for the bell to ring. The other switches will not affect the bell.