Q&A - PSLE Science

[tianzhu]

Rate of evaporation


One of the factors affecting the rate of evaporation is temperature.

When we are talking about temperature, does it refer to temperature of the source or temperature of the surroundings? For example a cup of hot water as compared to a cup of warm water in airconditioned/non airconditioned room, clothes left to dry under shade or out in the sun.
Please share your view.

[ChiefKiasu]

lizawa:

...

2. Yes. Bulbs arrange in parallel will shine brighter than bulbs arranged in series, with the same no. and battery arrangement. The current flowing through bulbs in series are lower due to higher resistance than the current flowing through bulbs in parallel.

3. No. same explanation as 2.

Oops. I didn't read question 2 properly. Looks like my son's carelessness is hereditary . Thought it was batteries in parallel rather than bulbs. Your answer for 2 is absolutely right.

But I stand by my answer for Q3. Batteries in parallel will last longer, assuming that the batteries are all of the same capacity.

[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…