- Six Diligence 2010

Friday, October 1, 2010 ; Yun Ling's Question and Answer

My answers are in red while her questions are in green or black.

When 2 batteries are in parallel, the amount of energy used for both batteries are the same, meaning both will be drained at the same time, not one at a time. Batteries in series makes the bulbs brighter. They're supplying more electrical energy but they might cause the bulbs to fuse if the electrical energy is too high.

but when 5 batteries are in parallel, you take out 4, won't there be a difference? But i always write that there will be no difference as i thought only drain from one battery.

If there isn't a difference when 4 are taken out, does that mean that they all add up to the electricity of one battery?

They last longer when they're in parallel. In terms of electrical energy provided at that point of use, there's no difference from 1 battery.

When do we use "-->" and "+" for energy conversion?

for example in the experiment where we put a paper ball on the spoon and bend the spoon. When bent further, the paper ball travels further.

so its:

EPE of the plastic spoon --> KE of plastic spoon + KE of paper ball

Why is it ''KE of plastic spoon+KE of paper ball'' instead of ''KE of plastic spoon-->KE of paper ball" Doesn't that make more sense as the KE of plastic spoon in the one that causes the paper ball to move?

The use of "+" and "-->" are not exactly that precise. Like you described, the KE of the paper ball can come from the KE of the plastic spoon. But then, the plastic spoon and the paper ball both move at the same time which was triggered by the EPE of the spoon. It can be both --> and + in this scenario. PSLE is more focused on the use of "-->" than "+" unless electricity is involved which is always "some energy+ heat energy".

Nuclear power plant
advantages: reduce its reliance on oil and natural gas, more environmentally friendly... etc.
disadvantages: no space to store spent fuel, highest construction cost. We have to know the energy conversions but the advantages and disadvantages?
Plus, is nuclear power plant in our syllabus? Cas i still don't get how it works :l sorry.

You're not needed to know how nuclear works or the advantages and disadvantages of all power stations but I'd say it is very helpful to know as they can provide information as ask about it. Anyway, just for knowledge, nuclear energy is a form of potential energy. So it goes like this

nuclear (potential) energy --> heat energy --> KE of air (boiling of water to steam) --> KE of turbine --> electrical energy

For decomposers, they break down dead materials to simple or simpler substances?

Simpler substances.

10) Why is there secondary consumers? I don't understand how come the can't be called tertiary consumers.
Primary consumers definitely must feed on food consumers, tertiary must feed on a food consumer. So what is the definition of secondary consumer, what is the difference between secondary consumer and tertiary consumers?

Primary consumers get energy from food producers. Secondary consumers are just consumers that get energy from primary consumers and tertiary consumers get energy from secondary consumers. Actually, they're not in your syllabus. It's just good to know how food web organisms are described as some of you read widely beyond the textbooks.

New Questions:

1) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/19823
A: Most birds lay eggs.
B: All birds care carnivorous.
C: Birds are warm-blooded.
D: Birds have beaks and feathers.
Isn't A,C,D all true? don't all birds lay eggs?
Yup, all birds lay eggs. Hence A is false because of the word "most".

2) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/18171
is this in syllabus? I dont understand why its fern
Neither do I. I know nothing about fern cells. This is not in syllabus. I don't know the answer myself :P

3) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/17970
cell wall, cell membrane, cytoplasm, i can't remember which one is semi-permeable... What is the cell membrane and cell wall for? i know that cell wall is for regular shape.
Cell wall is fully permeable while cell membrane is semi-permeable. Cytoplasm just contains whatever cell membrane allows in.
Cell membrane controls substances in and out of the cell. Cell wall gives support to the cell and the cell a regular shape.

4) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/19763
which part of the plant contains chlorophyll? i know the roots don't, flowers don't. But the stem does, doesn't it?
The stem of cactus do but most stems do not despite being green.

5) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/19764
A: Both X and Y are single-celled organisms.
B: Budding has taken place in both organisms.
C: The cells in both organisms X and Y have been fertilised.
D: Only one parent cell is required to produce 2 daughter cells.

A only (answer)
D only
A and D only
B and C only

Why isn't D correct?
For question on budding, the bigger cell after budding for Organism Y is the parent cell while the smaller one is the daughter cell, so D is wrong. This, however, is in your brother's syllabus, not yours.

6) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/20152
Just to clarify:
Ishak: From P to Q, there is an increase in height as the number of cells in the body increases.
Jena: From Q to R, there is no change in height because there is no cell division.
My answer: Cell division to replace dead or damaged cells, not for growth
Kathy: There is an increase in height from P to Q as the size of the cells in the body grows bigger.
My Answer: Increase in height is because there are more cells, but all cells do not grow

Are my answers correct? Yes, you're correct. Cells do not grow bigger. They grow in number, not size.

7) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/19824
I dont get this, what are they classifying it as?
By habitat, X is rotting log while Y is tree.

8) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/17987
Isn't this by body covering? then why lizard with seahorse?
Reptiles are covered by scales, as of fish. Reptile is not in your syllabus.

9) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/17990
C: Once alive
D: Never alive
for part (b), you once told us that there was no such classification as once alive and never alive, but we learnt it that way in P3?
Really? I've been told 6 years ago NEVER to teach like that. Please ignore such questions. :)

10) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/18157
(b) I choose material for paper as paper is light so it can float on the water but it absorb water, so after some time, it will be heavy and sink into the water.
Paper floats because wood floats (ignore absorbing water). True or false?
True. This is in the syllabus.

11) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/20056
aluminium is a poor conductor of heat? isn't it metal? :l
My answer is (4), all of the above. Aluminium is a good conductor of heat and it is important in all the 3 objects.
Aluminium drink can: Loses heat to cold air in fridge so drink can be cold
Foil and food container: Gain heat quickly from heat in oven so as to bake/heat up food

12) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/1ae7eed744e6441bcc3e2d1bf8dce67a/qn_id/18155
shouldn't Q be an insulator of electricity?
Yes, Q is insulator of electricity. I think there's an error in the answer key. It has happened in oldschool.com.sg before.

13) http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/19849
Its A and C right?
because theres the metal casing around that conducts electricity
Correct. IThey're circuits A and C.

14) Which one of the following is true?

A: all materials will absorb some light when light passes through
B: The ability of light to pass through can be further classified into 3 categories
C: for opaque objects, all light cannot pass through and is all reflected away
D: several pieces of translucent materials stacked together may become opaque altogether

ANS: A,B and D

A: Yes, even clear glass absorbs light, hence it can gain heat from light energy.
B: Yes, transparent, translucent, opaque
C: No, if light is completely reflected, it is a perfect mirror. If an object is green, green light is reflected into our eyes. The rest are absorbed. Bear in mind, green can come in many shades, so it's not just green reflected. This is not in the syllabus.
D: Yes, there's a PSLE Booklet question on this concept.

Other New Questions
1) Place a plant in blue coloured water and the stems and leaves will turn blue.
Why is it we always just write the flowers, we never do write that the stem turns blue as well.
Water-carrying tubes are inside the stem, so usually stems do not change colour easily.

as for this experiment they have one balsam plant in blue coloured water.
Aim: to find out if __Changed variable__ affects ___results____
So in this case the changed variable is the blue dye? results is stem and leaves turn blue?
But there isnt actually a changed variable is there? its only one set-up..
The aim can be anything. It could be whether balsam plant takes in blue water. It could be whether plants take in blue water. It could be whether plants take in coloured water. I mean the changed variable could be anything unless they provide one more set-up for comparison. Otherwise, they would have to accept any possible answer. Results could be leaves and flowers turn blue, unlikely to be stem. Flowers definitely.

Then what about control?
What is the purpose of the control and in the first place how should the control set-up be like?
Control would be balsam in clear water to check if the leaves and flowers turn blue without coloured water. I mean to put it stupidly, what if balsam turns blue without the use of blue colour? (Although we know it's not possible)

2) Then if there are two test tubes and both with a straw through the stopper, in the test tube one set-up has limewater, the other clear water
the aim is to find out if carbon dioxide turns limewater chalky, so shouldn't the other set up have nothing instead of water?
No. The use of limewater is to test for carbon dioxide. The second set-up is wrongly set-up. You should set up another one that uses limewater but for one set-up, carbon dioxide is blown into the straw. For the other, no blowing.

3) Does every experiment need a control? can a experiment only have one set-up?
Experiment may not need a control. An experiment might have only 1 set-up. For example, plant with 1 leaf wrapped with black paper but the rest not wrapped.

4) a sealed tank with water, fish and hydrilla
to find out: do the hydrilla and fish provide the gases and food for each other to survive?
is that even a proper experiment? there's no changed variable, no control, no comparism...
I'd say the aim is to find out if they can survive with each others' presence. In a way, it's a yes-no experiment. It's proper but it's a weird experiment.

5) Exhaled air:
1)contains more carbon dioxide than that of inhaled air (this is because inhaled in 0.03%, exhaled is 4%) <-- Not required to know exhaled %
2) contains water vapour
3) warmer than inhaled air
4) exhaled air 78% nitrogen 18% oxygen 4% carbon dioxide <-- Not required to know %

however, another workshee't's answer wrote:

The air we breathe in and out contains both oxygen and carbon dioxide.
The difference is:
1) we breathe in more oxygen than carbon dioxide (because 21% oxygen, 0.03% carbon dioxide?) <-- Required to know %
2) we breathe out more carbon dioxide than oxygen <-- this is wrong
Exhaled air contains more water vapour than inhaled air because of respiration

6) How does salt affect the boling points and freezing points of water?
I know it decreases the temperature of ice, but does it raise boiling point?
Salt reduces freezing point and raises boiling point but this is not in syllabus

7) 1000cm3 of air is drawn out from a hole on the cover of an 800cm3 glass cylinder. The hole was immediately sealed after the air was drawn out. What is the volume of air in the glass cylinder after 1000cm3 of air has been drawn out?
The answer is 800cm3
But how do we know that so much air is compressed in the cylinder? after removing 100ocm3 from a 800cm3 container how is there still 800cm3 left? Isnt that a little too much? or on the other hand there may be more, just that its compressed, do maybe another1000cm3 still can be drawn out?
Actually, there's no right and wrong answer as air has no definite volume. In a way, as long as there's air, the volume of air is the same as its container regardless of how much is pumped in or out.

8) When do we use ''it takes up space'' and when ''it has a definite volume'' when describing?
All matter has mass, so they take up space. Air is the only matter without definite volume. That's the main difference between these 2 descriptions.

Like for example there's a jar filled with water, when stones are added in, the water overflows. Which reason is it? I thought we should probably write both. Because if i write ''it takes up space'', its like all matter takes up space, so it doesn't really explain, but when i add in ''it has a definite volume'' it means that it cannot be compressed so it will take up that space and there will be no space for the water... something like that.

So can i write both? Some of the answer sheets wrote takes up space, some wrote has a definite volume. both were describing solids.
Yes, you can write both. I'd say it's safer to write both. I might even write that water cannot be compressed, so it overflows.
My Answer: Stones take up space and has definite volume. When stones are added, the same volume of water is displaced out of the jar as both have a definite volume and cannot be compressed.

Regards,
Mr Wan

posted by Allan at 10:51 PM

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