Q&A - PSLE Science

[lizawa]

tianzhu:

Hi lizawa


Thanks for sharing.

If the bread is dried, mould will not develop over time. However, the question did not state if the bread was hot or cold when placed in the container. Should bread be enclosed in a container straight from the oven, water droplets would appear, causing mould to develop?

The question then will be whether the condensed water droplets are sufficient to turn the bread mouldy or whether the high temperature of the oven will kill the fungi and therefore no bread mould will be formed even if there is some water present.

This is why cookies made by loving mothers/wives and not forgetting some fathers during Chinese New Year are left to cool before packaging. Interesting indeed.

you are right. if it is cooled down then left in air tight container, mould will not develop. but if it is put in when hot, then, maybe mould will be formed. so how to answer this question ? maybe the child needs to put in the qualifier first. I did notice that sometimes even for a 2 mark question, the expectation is quite a lot to get the full 2 marks.
Y

[tianzhu]

lizawa:

I did notice that sometimes even for a 2 mark question, the expectation is quite a lot to get the full 2 marks.

It’s difficult to know what went through the mind of the question setter. There are certainly some alternative answers if you look at this question through different angles.

Perhaps, we should state some assumptions before going on to answer the question. Yes, it’s tough getting those marks. Putting in the right details is indeed challenging.

[tianzhu]

Rate of Evaporation


Q1) Why do you feel cool when you stand next to a fan?

Q2) Many people are familiar with the daily routine of washing, drying, and styling their hair. Have you ever wondered what are the factors affecting the speed of drying up your hair?

[ChiefKiasu]

tianzhu:

Rate of Evaporation


Q1) Why do you feel cool when you stand next to a fan?

Q2) Many people are familiar with the daily routine of washing, drying, and styling their hair. Have you ever wondered what are the factors affecting the speed of drying up your hair?

A1) Fan produces air movement which accelerates process of moisture evaporating from human skin, which in turn lowers the temperature as heat is absorbed to transform water to vapor.

A2) Factors
- Wind
- Heat
- Surface area

[lizawa]

ChiefKiasu:

tianzhu:

Rate of Evaporation


Q1) Why do you feel cool when you stand next to a fan?

Q2) Many people are familiar with the daily routine of washing, drying, and styling their hair. Have you ever wondered what are the factors affecting the speed of drying up your hair?

A1) Fan produces air movement which accelerates process of moisture evaporating from human skin, which in turn lowers the temperature as heat is absorbed to transform water to vapor.

A2) Factors
- Wind
- Heat
- Surface area

For A2, how will humidity of the surrounding affect the speed of drying up your hair ? Thinking along the line of the 4 factors that affect speed of evaporation.

[csc]

lizawa:

ChiefKiasu:

[quote=\"tianzhu\"]Rate of Evaporation


Q1) Why do you feel cool when you stand next to a fan?

Q2) Many people are familiar with the daily routine of washing, drying, and styling their hair. Have you ever wondered what are the factors affecting the speed of drying up your hair?

A1) Fan produces air movement which accelerates process of moisture evaporating from human skin, which in turn lowers the temperature as heat is absorbed to transform water to vapor.

A2) Factors
- Wind
- Heat
- Surface area

For A2, how will humidity of the surrounding affect the speed of drying up your hair ? Thinking along the line of the 4 factors that affect speed of evaporation.[/quote]The lower the humidity of the surrounding, the higher the rate of evaporation. The speed of drying up hair will hence increase.

[lizawa]

csc:

lizawa:

[quote=\"ChiefKiasu\"]
A1) Fan produces air movement which accelerates process of moisture evaporating from human skin, which in turn lowers the temperature as heat is absorbed to transform water to vapor.

A2) Factors
- Wind
- Heat
- Surface area

For A2, how will humidity of the surrounding affect the speed of drying up your hair ? Thinking along the line of the 4 factors that affect speed of evaporation.

The lower the humidity of the surrounding, the higher the rate of evaporation. The speed of drying up hair will hence increase.[/quote]So, assuming all factors remain the same, drying your hair in an air-con room will be faster than that in a non air-con room.

[Emelyn]

I feel very stressed after reading all the posts here.

All of you are so knowledgeable.

My son is P4 this yr…

which makes me even more stress.

very chim questions and answers…

[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.

[ChiefKiasu]

Emelyn:

I feel very stressed after reading all the posts here.

All of you are so knowledgeable.

My son is P4 this yr.......

which makes me even more stress.

very chim questions and answers.....

One trait of successful people is their ability to network and learn from other successful people. That's exactly what we are trying to do here, to create an environment where parents can come and learn from other parents who may have more experience. We are fortunate to have so many parents such as tianzhu, lizawa, tamarind, chamonix, insider, buds etc who are selfless in sharing their own parenting experiences so that we can all learn to be better parents to our children. It is not about how much more we know compared to others. The more we share, the more we learn.

Such threads where questions are posed and answered by others in the community are useful so that we know for ourselves what we are asking our own children to do. So many times I have heard parents yell at their kids: \"How come u so stupid arh? Cannot even score Band 1 for XYZ?!\" If roles were switched, I wonder if they can do what they are telling their children to do themselves.

And if our children are having difficulties and we ourselves are unable to help them, then, as responsible parents, we need to think of alternative ways of helping them such as enrichment programmes or tuition. If we can do it ourselves, then we can save money and be better equipped to know how to help them by learning from these questions and answers that are posted.