Q&A - PSLE Science

[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.

[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.

[ChiefKiasu]

lizawa:

...

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.

Thanks lizawa, I forgot about the humidity. Guess I have to start reading my son's science books :).

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

[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.