Tutor Niedino: Pri Science Questions and Concepts

[Dharma]

rkumar:

HaleyCopterz:

[quote=\"rkumar\"]
Hi,

We do not say that a material is an 'insulator of heat' that would be marked wrong. Nothing is an insulator of heat as everything can conduct heat to a certain degree. So we should say that metal is a better conductor of heat than plastic. If a material is a better conductor of heat, that means heat travels through that material very quickly.

Hi Haleycopter and Bigdad

insulator of heat is indeed a valid term. Poor conductors of heat are good insulators of heat and vice versa. i believe it is still covered in the \"o\" level syllabus. \"Plastic\" heat properties question came out 2004 'O' level physics exam. Good Insulator/poor conductor both accepted.:D

I think you may have mistaken insulation to mean stop heat altogether.

definition i found on a website

Substances that do not conduct heat well are called insulators. The word insulator comes from the Latin word insula, which means island. Insulators have a low coefficient of conductivity; they do not conduct heat well. Nonmetals, such as wood, textiles, and plastic, are usually poor conductors. Gases are also poor conductors.

[/quote]For PSLE Science, I remember my dds Science teachers’ telling them not to use “insulator”……

Always use good conductor of heat or poor conductor of heat

or

Object A is a better conductor of heat than object B

Or

Object B is poorer conductor of heat than object A

[atutor2001]

There are other terms that must never be used. Another one is never use \"coldness\" - use loses heat. Oh no, my mind is blank. Will post more when I remembered. :oops:


Another one : Never use \"grow\" for non-living things such as metal when heated or shadow - use \"expands\" for metal and \"become\" for shadow.

Don't use \"soft\" if you need the material to bend - use \"flexible\"
Don't use \"flexible\" if you need the material to stretch - use \"elastic\"

[rkumar]

Dharma:

rkumar:

[quote=\"HaleyCopterz\"]

For PSLE Science, I remember my dds Science teachers’ telling them not to use “insulator”……

Always use good conductor of heat or poor conductor of heat

or

Object A is a better conductor of heat than object B

Or

Object B is poorer conductor of heat than object A

[/quote]


Thanks Dharma and Haley,

My nephew did his P5 CA2 recently. Some question relating to thermos flask and why they can keep heat longer. He answered it correctly quoting poor conductor of heat. Got one 1 mark out of 2. When my sister asked the teacher. the Teacher told her (very curtly) that the appropriate answer would be to talk about the insulating properties of the flask. My sister has a bone to pick with her since.

being the ignoramus as i was, told her to leave it, as i thought the teacher was right.

Now that i know that its officially discouraged in other schools...... :x. Lets just say the teacher is gonna need all the \"insulation\" she can get her hands on.

Appreciate your timely comments. You people rock!

[rkumar]

atutor2001:

There are other terms that must never be used. Another one is never use \"coldness\" - use loses heat. Oh no, my mind is blank. Will post more when I remembered. :oops:


Another one : Never use \"grow\" for non-living things such as metal when heated or shadow - use \"expands\" for metal and \"become\" for shadow.

Don't use \"soft\" if you need the material to bend - use \"flexible\"
Don't use \"flexible\" if you need the material to stretch - use \"elastic\"

Good list of words. I can see how the students might make the mistakes. Will be very useful for my son doing P3 now. Thanks

[atutor2001]

rkumar:

Thanks Dharma and Haley,

My nephew did his P5 CA2 recently. Some question relating to thermos flask and why they can keep heat longer. He answered it correctly quoting poor conductor of heat. Got one 1 mark out of 2. When my sister asked the teacher. the Teacher told her (very curtly) that the appropriate answer would be to talk about the insulating properties of the flask. My sister has a bone to pick with her since.

being the ignoramus as i was, told her to leave it, as i thought the teacher was right.

Now that i know that its officially discouraged in other schools...... :x. Lets just say the teacher is gonna need all the \"insulation\" she can get her hands on.

Appreciate your timely comments. You people rock!

Hi rkumar

Hate to add to the confusion but the teacher's answer is correct in this case.

The question is not testing on \"heat conductivity of a material\". The topic tested is \"insulating property of vacuum (no material in between)\" i.e. heat cannot be conducted if there is no material (air) in between. Heat cannot pass through a thermo flask because the inner layer and outer layer are separated by a vacuum. Therefore, vacuum can insulate heat. So we need to apply different concept for this question.

Regards

[Dharma]

Slides 15 to 19 may interest some of you.


http://www.yewteepri.moe.edu.sg/uploads/P6%20Science.pdf

[rkumar]

hi atutor,


Thanks for your input.
My mistake for adding thermos to flask. It was not a vacuum(thermos) flask. it was a flask, diagram (cross section). The walls were hollow and filled with air.
The question was why it could retain heat better than the other container (flask) same material no air in between.

In any case whats with the 1 mark. you either give the 2 marks or nothing at all. Another thing that i have to clarify with her.

cheers

[snowman.022851697]

For 2-mark explanation questions, first you explain your answer, then explain why the other options/possibilities are not the answers.

[Tang]

rkumar:

Dharma:

[quote=\"rkumar\"]



Thanks Dharma and Haley,

My nephew did his P5 CA2 recently. Some question relating to thermos flask and why they can keep heat longer. He answered it correctly quoting poor conductor of heat. Got one 1 mark out of 2. When my sister asked the teacher. the Teacher told her (very curtly) that the appropriate answer would be to talk about the insulating properties of the flask. My sister has a bone to pick with her since.

being the ignoramus as i was, told her to leave it, as i thought the teacher was right.

Now that i know that its officially discouraged in other schools...... :x. Lets just say the teacher is gonna need all the \"insulation\" she can get her hands on.

Appreciate your timely comments. You people rock!

[/quote]Hi,

For a 2-mark question, one can't expect to get full mark by just stating that it is a poor conductor of heat.

You need to elaborate further....

In fact 'a poor conductor of heat' is not a complete answer, comparison is required since question stated 'keep heat longer'.

It slows down the heat loss better from the hot water to the surroundings.

Hope it is useful and timely for the PSLE 2010.

[yongjianrong]

Just found some confusing concepts.


1. When something is at a greater height, it has more gravitational potential energy but the gravity pull is weaker, why is that so?

2. Do we consider 'air resistance' as 'friction'?

3. a) When duckweeds cover the surface of pond completely, do they literally mean that there is no gap between each duckweed?

b)If so, will fishes suffocate? I have one revision paper which says the fish will suffocate. However, when duckweeds photosynthesise, they will produce oxygen and the oxygen will also exit through the stomata on the underside of the leaves followed by entering the pond. So how can the fishes suffocate?