## Section B (open ended questions) for science

Discussions on tuition centres/enrichment services that specialise in Science enrichment programmes
Andrea D
OrangeBelt
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### Re: Section B (open ended questions) for science

Thank you for sharing that wynea. This is an interesting discussion and it can really depend on a lot of factors.

Did your son improve his grade through the home tuition though? Maybe he just wasn't excited about extra work at home, or perhaps the tutor couldn't adapt the right relationship for work with him.

Do you know which exact classes your daughter went on in CCE?

IreneK
YellowBelt
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### Re: Section B (open ended questions) for science

szepinge wrote:
Thu Mar 08, 2018 11:03 pm
Anyone keen to enrol in my March holiday course or Regular science courses
Revision for P3-P6 concepts
Section A and Section B answering techniques
Kindly visit my blog at
www.mdmchewscience.blogspot.com
email : szepinge@yahoo.com.sg
I’m a NIE trained science teacher.
Have been teaching science for 18 years
particularly p6 students through their psle.
Thank you for sharing

twinningtalks
KiasuNewbie
Posts: 1
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### Re: Section B (open ended questions) for science

I need help on the rationale behind why the answer is (3) for the below question. If the answer is (3), the principle "Air can be compressed" does not apply to the balloon. So which principle explains and support the answer below. Thank you so much.

Iluvmygals
OrangeBelt
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### Re: Section B (open ended questions) for science

twinningtalks wrote:
Fri May 17, 2019 12:02 am
I need help on the rationale behind why the answer is (3) for the below question. If the answer is (3), the principle "Air can be compressed" does not apply to the balloon. So which principle explains and support the answer below. Thank you so much.

1. While air can be compressed in the balloon, we don't know how much it will be compressed...so it can be 320, 380 etc. So straight away choice 1 & 2 can be eliminated.
2. So left choice 3 & 4 to choose from. So since the glass ball is fixed shape and volume, the answer is 3.

wella88
KiasuNewbie
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### Re: Section B (open ended questions) for science

Iluvmygals wrote:
Fri May 17, 2019 6:29 am
twinningtalks wrote:
Fri May 17, 2019 12:02 am
I need help on the rationale behind why the answer is (3) for the below question. If the answer is (3), the principle "Air can be compressed" does not apply to the balloon. So which principle explains and support the answer below. Thank you so much.

1. While air can be compressed in the balloon, we don't know how much it will be compressed...so it can be 320, 380 etc. So straight away choice 1 & 2 can be eliminated.
2. So left choice 3 & 4 to choose from. So since the glass ball is fixed shape and volume, the answer is 3.
Thank you, iluvmygals

mummy musings
KiasuNewbie
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### Re: Section B (open ended questions) for science

twinningtalks wrote:
Fri May 17, 2019 12:02 am
I need help on the rationale behind why the answer is (3) for the below question. If the answer is (3), the principle "Air can be compressed" does not apply to the balloon. So which principle explains and support the answer below. Thank you so much.

Hi wella! Is your child in P3? I remember seeing a similar question in one of my DS’s homeworks.

Anyway, back to your question. Air has no definite volume; it takes the shape of the container. This means it can be compressed to occupy a smaller space. It also can expand to take up a bigger space.

A balloon is made of material which can be stretched. When you blow air into the balloon, it’ll expand. As more air is blown into the balloon, its volume increases until it finally bursts. The glass ball cannot be stretched when additional air is pumped into it. Hence the air is compressed. The balloon can be stretched to accommodate the extra air, hence the air expands to take the shape of the stretched balloon.

Therefore, Option (3) is correct. Hope this helps!

realtalk
YellowBelt
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Joined: Wed Jul 12,

### Re: Section B (open ended questions) for science

twinningtalks wrote:
Fri May 17, 2019 12:02 am
I need help on the rationale behind why the answer is (3) for the below question. If the answer is (3), the principle "Air can be compressed" does not apply to the balloon. So which principle explains and support the answer below. Thank you so much.

Hello! I got confused at first with the question. I even asked my elder daughter to check it for me

Setup A, the glass ball cannot be expanded. When the plunger is pushed, the 100 cm of air entering the glass ball is compressed into the 300 cm of space in the glass ball (note: gas does not have definite volume and can be compressed)

Setup B, the balloon can be inflated. When the plunger is pushed, the 100 cm of air is pushed into the balloon causing it to inflate and since the balloon can be inflated, it will take up the additional 100cm of space (300 + 100). Hope this helps!

floppy
KiasuGrandMaster
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### Re: Section B (open ended questions) for science

twinningtalks wrote:
Fri May 17, 2019 12:02 am
I need help on the rationale behind why the answer is (3) for the below question. If the answer is (3), the principle "Air can be compressed" does not apply to the balloon. So which principle explains and support the answer below. Thank you so much.

Can even expand this question to become a O level question

What's the pressure of the air in the glass ball and in the balloon after the plungers are pushed all the way, relatively to their original pressure?

.zeit
BlueBelt
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### Re: Section B (open ended questions) for science

Refrain from imposing our O and A level science or even engineering / medical knowledge on our PSLE kid. Over-teaching concepts outside of PSLE syllabus may confuse average kids and jeopardise their grades.

Iluvmygals
OrangeBelt
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### Re: Section B (open ended questions) for science

Sometime the choices in the MCQ are not the "real" answers. In this balloon case, the volume of air in the balloon after the plunger is pushed may not be 400 cause while the balloon can expand, it can also compress the air too since the balloon is elastic. So the "real" volume can be anything between 300 - 400 depending on how stretch is the balloon. So for the kids, this might be overthinking the question.

This MCQ basically test 2 things:
1. Air has no fixed volume, hence in the glass container, the air volume does not increase even when the plunger is pushed.

2. Balloon can be stretch when more air is pumped in. Hence any air pumped in will fill up the volume.

Typically I would ask my kids to cancel out 2 choices based on what they definitely know. So here my kids would know that volume in the glass container is definitely 300. So can eliminate choice 1 and 4. Then with the remainder 2 choices they will decide what happens in the balloon. So the balloon can stretch when air is pumped in, so its volume will not be 300. Hence the answer is 3.

So for MCQ, sometimes it may not be choosing the right answer. We can also answer by eliminating the wrong choices.