Q&A - PSLE Science

[lizawa]

ChiefKiasu:

BTW... do you agree with my point regarding the batteries in parallel lasting longer?

I am not too sure about this one. Is the amount of electricity discharged per cycle of the battery dependent on the battery arrangement ?

[ChiefKiasu]

lizawa:

I am not too sure about this one. Is the amount of electricity discharged per cycle of the battery dependent on the battery arrangement ?

See this http://www.teachengineering.org/view_activity.php?url=http://www.teachengineering.org/collection/wpi_/activities/wpi_ohm_2/wpi_ohm2_act_joy.xml.

Quote:
\"The batteries in a series will give a brighter light; however will last about ½ the time of batteries in parallel.

Batteries set up in a parallel circuit will give a less intense light, but will last 2x the length of batteries in series.\"

Of course, the assumption in the above statement is that the number of batteries used is 2.

[tianzhu]

ChiefKiasu:

tianzhu:

Evaporation and Condensation


Your loving mother put some hot Tiong Bahru Paos (buns) in a transparent plastic hood. After a few minutes , water droplets are observed to be formed on the inner surface of the hood. Is it right to say that hot water vapours from the paos (buns) condensed into water droplets when they touched the cooler interior surface.

Likewise for a cup of hot coffee, placed under a hood, is it right to say that hot water vapours from the coffee condensed to form water droplets. Similarly for rice cooking, it is more appropriate to use steam or hot water vapours when explaining about condensation at the inner lid of the rice cooker.

The heated water in the paos is transformed to the gaseous state as steam. When steam gets in contact with cool surfaces such as the plastic hood, it cools and transforms back into the liquid state. This forms the water droplets on the underside of the plastic hood covering the hot paos.

It may not be appropriate to use use steam in this instance.The buns may be hot, but it's not at boiling point.In this example, we are talking about hot buns placed in a hood to prevent contact with insects/flies.

I am trying to establish the more appropriate words to use to answer the questions under varying circumstances.Some markers may be very strict.

[lizawa]

tianzhu:

ChiefKiasu:

[quote=\"tianzhu\"]Evaporation and Condensation


Your loving mother put some hot Tiong Bahru Paos (buns) in a transparent plastic hood. After a few minutes , water droplets are observed to be formed on the inner surface of the hood. Is it right to say that hot water vapours from the paos (buns) condensed into water droplets when they touched the cooler interior surface.

Likewise for a cup of hot coffee, placed under a hood, is it right to say that hot water vapours from the coffee condensed to form water droplets. Similarly for rice cooking, it is more appropriate to use steam or hot water vapours when explaining about condensation at the inner lid of the rice cooker.

The heated water in the paos is transformed to the gaseous state as steam. When steam gets in contact with cool surfaces such as the plastic hood, it cools and transforms back into the liquid state. This forms the water droplets on the underside of the plastic hood covering the hot paos.

It may not be appropriate to use use steam in this instance.The buns may be hot, but it's not at boiling point.In this example, we are talking about hot buns placed in a hood to prevent contact with insects/flies.[/quote]When the buns are heated, they have a higher temperature than the surrounding air. The heat will travel from the hotter object (bun) to the colder surrounding air. (concept of heat conduction). This will cause the water vapor to gain heat. When the water vapour touches the underside of the plastic hood (which is cooler), it will lose its heat and condenses, hence forming water droplets.

[tianzhu]

Respiratory/circulatory systems


In this question, there was a table showing the composition of three air samples. The volume of each sample is 100 cubic centimeter.

Part B of the question asked which activity used up more oxygen, sleeping or running. Explain your answer. (1 mark)

The following answer was given zero marks. ----- Running. When we are running, our lungs need to take in more oxygen so that the heart can pump more blood containing oxygen and digested food to the various parts of the body to produce the amount of energy needed.

What is the more appropriate answer?

[lizawa]

tianzhu:

Respiratory/circulatory systems


In this question, there was a table showing the composition of three air samples. The volume of each sample is 100 cubic centimeter.

Part B of the question asked which activity used up more oxygen, sleeping or running. Explain your answer. (1 mark)

The following answer was given zero marks. ----- Running. When we are running, our lungs need to take in more oxygen so that the heart can pump more blood containing oxygen and digested food to the various parts of the body to produce the amount of energy needed.

What is the more appropriate answer?

Running. More oxygen is needed to break down the digested food to produce more energy for the activity.

NB : No mark is given for \"running\" if the explanation is incorrect. This is what I understand from the science teacher with regards to how strict the marking for the Science paper open ended question is.

BTW : Tianzhu, it will be good if you can also provide some \"model answers\" from the teacher for all these questions. Good reference for us. Thanks !

[tianzhu]

Hi lizawa


Questions concerning chestnuts and hair dryer are conceived through observation of some regular activities. As for the question on breathing/heart beats, there are varied explanations and I am still searching for the most suitable one.

I try to keep updated by reading some assessment books, so that I can help my son when he faces difficulties.

I put up this thread to create more awareness about Primary Science questions, and to serve as a platform for discussion on the ways to tackle them. Hopefully, through brainstorming and piggy-back on each other’s view, we are able to arrive at some fruitful answers.

[tianzhu]

Hi lizawa,


I am still trying hard to understand the relationships between circulatory and respiratory systems, and to put in the relevant information to secure precious marks.You are right to say that marking is stringent.

Two popular types of questions are why there are increase in breathing rates and heart beats during exercises.

Fortunately, there is still time, and hopefully we can have the most appropriate before PSLE Science exam.

[caroline3sg]

tianzhu

Personally I think assessement books are not enough. You need to get guide books. I usually get many types.

I am impressed with ChiefKS’s & Lizawa’s answers to the questions that you have put up. We may know the answer but to put them in proper and convincing way is not easy.

With regards to the zero mark for running …, this answer was given in P4 syllabus, while Lizawa’s answer is based on P5 syllabus, which I think MOE / Science syllabus should not be half here and half there.

[caroline3sg]

Regarding the mould on bread question, this was 2007 PSLE question. It appeared in ST Forum to MOE.