Q&A - P3 Science

[Happy Mama]

pingathot:

Hi parents, m shocked to c the questions asked abt magnet 'cos for P4 they've not taught yet. U meant u parents have already get your children to do the papers in advance? Oh mine, then I must b lacking bhind.

Yes I think different schools cover differently. My Pri 3 DD will be covering Magnets in Term 4 this year.

[teh_oh]

atutor2001:

teh_oh:

Why didn't that surface of the iron tank that is in contact with the magnet, have temporary magnetism through 'induction' (as in the first diagram) to attract the steel ball bearing?

Why nowadays no respond one?

Anyway, you are correct that the \"ENTIRE\" surface of the iron tank will become a temporary magnet due to induction. However, it has very weak magnetic force. The magnetic force from the small bar magnet is used to re-align all the \"little magnets\" in the tank (to north-south direction). With such a large tank, the magnetic force cannot completely re-align all the \"little magnets\" in the tank. Many of the \"little magnets\" in the tank are still not aligned and so the magnetic force of the tank is weak.

If we use a \"super\" strong magnet, the steel ball bearing will be stuck to the surface of the iron tank.

Hi atutor2001,
Thank you for the explanation.

[teh_oh]

Hi,

Relating to magnets again, I need to know if the guide/assessment book is wrong or our concept is wrong:-
http://i56.tinypic.com/xpuhk3.jpg\">
The above is from a guide book.
Are the poles wrongly stated? Compare to the diagram in
http://www.le.ac.uk/se/centres/sci/selfstudy/mam9.htm
the poles stated in the guidebook is different.
Based on single-stroke method, during stroking, when the North-pole of the magnet when lifted off the head of the nail, the polarity of that nail at the head should be South.
Am I right?

http://i54.tinypic.com/2r779qt.jpg\">
The above is taken from an assessment book by the same publisher of the guide in the first picture.
The above question answer key is 3. Correct or wrong?

Thank you.
(We have given up seeking info from the science teacher because the teacher's replies had been 'go and check the internet', 'have i taught this already/before?' and when asked if key words or answering technique will be taught,'everything is taught in class. students who pay attention should know.')

[atutor2001]

Hi teh_oh


You are correct that the nail head should be S and the answer to that question should be (1).

[tianzhu]

Hi teh_oh


Way of making magnet ----- Stroking

I think stroking is one of the ways of making magnets as described in primary science. It‘s not covered in great details.

I am not too sure if students are required to find out the polarities of magnets produced by single or double stroking method. It may not be in the syllabus. Please check with the school.

Out of curiosity, I checked my boy’s book, Physics Matter.
There is a small topic on “Stroking”
It states “The pole produced at the end of the steel bar where the strokes finish is opposite to the stroking pole used”

You may also read these two interesting sites.

http://www.tutorvista.com/content/physics/physics-i/magnetism/magnetization.php

http://docs.google.com/viewer?a=v&q=cache:VvzUOh8HgLcJ:www.mai-edu.net/LessonFilesDel/Unit%252016%2520-%2520Magnetism.ppt+www.mai-edu.net/LessonFilesDel/Unit+16+-+Magnetism.ppt&hl=en&gl=sg&pid=bl&srcid=ADGEESiPfXZ8w8Onj8rBqh7F3t4iWinNIac3luAVNk0g_XTw5vNX9ZFM2dFJptqk7i1SrrVNvaiy-UuXBvf960Y3B49in-U63yzOMMkL-nbEk3PywYpnnEhSmD8XcWRh5N3DvcFNBao7&sig=AHIEtbRyP1nMuD8kADv4b_QM7n19QyxLNg

For the second site, please refer to page 52 and 53.

Best wishes

[teh_oh]

atutor2001:

Hi teh_oh


You are correct that the nail head should be S and the answer to that question should be (1).

Hi atutor2001,
:thankyou:

[teh_oh]

tianzhu:

Hi teh_oh


Way of making magnet ----- Stroking

I think stroking is one of the ways of making magnets as described in primary science. It‘s not covered in great details.

I am not too sure if students are required to find out the polarities of magnets produced by single or double stroking method. It may not be in the syllabus. Please check with the school.

Out of curiosity, I checked my boy’s book, Physics Matter.
There is a small topic on “Stroking”
It states “The pole produced at the end of the steel bar where the strokes finish is opposite to the stroking pole used”

You may also read these two interesting sites.

http://www.tutorvista.com/content/physics/physics-i/magnetism/magnetization.php

http://docs.google.com/viewer?a=v&q=cache:VvzUOh8HgLcJ:www.mai-edu.net/LessonFilesDel/Unit%252016%2520-%2520Magnetism.ppt+www.mai-edu.net/LessonFilesDel/Unit+16+-+Magnetism.ppt&hl=en&gl=sg&pid=bl&srcid=ADGEESiPfXZ8w8Onj8rBqh7F3t4iWinNIac3luAVNk0g_XTw5vNX9ZFM2dFJptqk7i1SrrVNvaiy-UuXBvf960Y3B49in-U63yzOMMkL-nbEk3PywYpnnEhSmD8XcWRh5N3DvcFNBao7&sig=AHIEtbRyP1nMuD8kADv4b_QM7n19QyxLNg

For the second site, please refer to page 52 and 53.

Best wishes

Hi Tianzhu,
Thank you too.
For finding out the polarity, my child got it correct. I got thrown off by the wrong answer in the assessment book AND the wrong annotation in the guidebook. Not sure if it is in the syllabus, but such questions came out in two different assessment books that I have.

Thank you again for the information attachments.

[tianzhu]

teh_oh:

Hi Tianzhu,

Thank you too.

Hi

You're welcome.

Best wishes

[rrjan]

Hi, could any of the science gurus here kindly render me some help with this question?


James carried out an experiment by using water and sugar. He placed 2 petri dishes in the same place. He then recorded his observations in the table below at the end of each day.

Petri dish X contains water.
Day 1 - Bacterial growth +
Day 2 - Bacterial growth +
Day 3 - Bacterial growth +

Petri dish Y contains sugar
Day 1 - Bacterial growth +
Day 2 - Bacterial growth ++
Day 3 - Bacterial growth +++

Which one of the 2 substances would you use to speed up bacterial growth? Explain why you have chosen this substance.

My son chose the substance sugar. His explaination is that bacterial likes sugar.

Think this is not the correct way of explaining the reason for his choice, right? How should we state our explaination ?

Any kind help is sincerely appreciated. Thanks

[tianzhu]

Hi


One observes that the difference between set up X and set up Y is that the Petri dish Y contains sugar.

Based on the given data, one can see that the bacteria growth in dish Y is increasing as highlighted by the number of plus signs (+) as compared to dish X which stays the same.

So, one can infer that sugar helps bacteria growth.

I’d choose sugar. The bacteria growth is increasing in dish Y as compared to dish X which remains the same. It shows that sugar speeds up bacterial growth.

Best wishes