Q&A - P3 Science

[tianzhu]

Hi


Well, for experiments, we have to accept the fact that there would be experimental errors. We have to make allowances for differences in readings, something like parallax error in reading of measurements, or reaction to stopping of stop watches. This will lead to discrepancies in readings.

In this particular case, marginal differences in timings will not significantly affect the outcome. Yes, the teacher is right to take the average reading. And 31 is close enough to 31.5, don’t you think so?

[kitty2]

Are silkworms an insect?From the answer sheet,the answer is ,Yes. :?

[atutor2001]

kitty2:

Are silkworms an insect?From the answer sheet,the answer is ,Yes. :?

Yes it is the young (larva) of a kind of moth.

[Lynn2]

Hi Tianzhu


Thanks for the pointers.

Hey, for the same acs paper http://www.wendykoh.com/08/primary4-acssa2-science.pdf

Can someone explain, why question 16,the answer is 3?as in DABC and not DABC?

Also , question 28,why is the answer 4 and not 2?

thanks and have a good holidays all...

tianzhu:

Hi

Well, for experiments, we have to accept the fact that there would be experimental errors. We have to make allowances for differences in readings, something like parallax error in reading of measurements, or reaction to stopping of stop watches. This will lead to discrepancies in readings.

In this particular case, marginal differences in timings will not significantly affect the outcome. Yes, the teacher is right to take the average reading. And 31 is close enough to 31.5, don’t you think so?

[Lynn2]

just wonder, why my girl keeps insist that dragonfly lays eggs on land,anyone can explain?thanks

Lynn2:

Hi Tianzhu

Thanks for the pointers.

Hey, for the same acs paper http://www.wendykoh.com/08/primary4-acssa2-science.pdf

Can someone explain, why question 16,the answer is 3?as in DABC and not DABC?

Also , question 28,why is the answer 4 and not 2?

thanks and have a good holidays all...

[Lynn2]

another question from taonan


http://www.wendykoh.com/08/primary4-taonansa2-science.pdf

can check with ks members here on two questions that related to evaporation.

QUESTION 41,Why is it not possible to tell the wind caused the rate of drying to increase in all the towels and also why towel b will absorb the most amount of water.

Question 44 why there is no change in water level after the beakers are out in the sun for four hours when there are different rate of evaporation takes place?thanks

[tianzhu]

Hi


Q28) Follow these links, they should help to address your query on dragonfly.
http://www.dragonfly-site.com/dragonfly-life-cycle.html
http://www.blithfieldeducationcentre.co.uk/kp/environmentpages/dragonfly_life_cycle.htm

For Q16, option(3) is a logical answer.
D and A are pretty obvious, they are nearer to the heat source. B will be the next one because it is found in the same bar, allowing heat to reach it first as compared to C. As for C, heat has to be conducted through the T junction; therefore a longer time is needed to melt the wax than B.

[Lynn2]

Hi Tianzhu


Thanks for the link and explanation...you have taught me so much...thank you.

rgds

tianzhu:

Hi

Q28) Follow these links, they should help to address your query on dragonfly.
http://www.dragonfly-site.com/dragonfly-life-cycle.html
http://www.blithfieldeducationcentre.co.uk/kp/environmentpages/dragonfly_life_cycle.htm

For Q16, option(3) is a logical answer.
D and A are pretty obvious, they are nearer to the heat source. B will be the next one because it is found in the same bar, allowing heat to reach it first as compared to C. As for C, heat has to be conducted through the T junction; therefore a longer time is needed to melt the wax than B.

[tianzhu]

Hi


For the third statement, Towel B will absorb the most amount of water.
My take is not possible to tell.

This experiment is to show whether the exposed area of a towel affects the rate of evaporation. For a fair test, the amount of water absorbed by the towels must be the same at the starting point.

The question did not show how the towels get wet, that is, how the towels are dipped in water.

Consider scenario1 – The towels are folded first as in A,B,C and D before dipping into a container of water big enough to accommodate a fully stretched out one, Towel B. In this case, there is a likelihood of Towel B absorbing the most amount of water as compared to the others because of a larger exposed area.

Consider scenario 2 – The towels are dipped in exactly the same way. In this way, the chance of all towels absorbing the same amount of water is high. In both scenarios, the duration remains the same.

As for the last statement, the key word lies in based on the experiment above. From background knowledge, we know that higher wind speed increases the rate of evaporation. But, there is no mention of wind speed in this question, so we cannot infer that the wind caused the rate of drying to increase.

Maybe to elaborate further, consider a real life example.
Lucy has a beautiful daughter. Let’s call her Linda
Linda appeared in a dialogue on radio. She spoke eloquently in a clear and sweet voice.
Based on the radio programme, for listeners (yet to see Lucy’s daughter), they can only say that Linda spoke well and has a sweet voice. I am not sure whether this is a good example but hope it’ll help you.

For these types of questions, we have to exercise caution not to input background knowledge.

Best wishes.Have a nice weekend.

[tianzhu]

Hi

[quote]Question 44 why there is no change in water level after the beakers are out in the sun for four hours when there are different rate of evaporation takes place?[/quote]Yes, if you look carefully, you can see that there is an attempt by the the answerer of the WS to differentiate the differences in the level of liquids.
The 150 cubic cm is just an indication on the measuring cylinder. Look at those measuring cylinders you used for cooking, I am sure you can see those markings.

The concept is more evaporation means less remaining liquid. Apply it; A has the lowest remaining level, followed by C and B