Q&A - PSLE Science

[tianzhu]

wkong:

Thanks ADoc for the explanation of the questions I posted earlier on.


I have another question that I need advice:

The answer is (3) or (4)?


http://postimage.org/image/1sz47y62s/

Hi

I cannot remember seeing term like magnetic energy in PSLE science under the topic of Energy.

The forms of energy are Potential, Kinetic, Heat, Light, Sound and Electricity.

Best wishes

[anneshirleygilbert]

Need some help for this question on heat:


In which of the following will the milk gain the most amount of heat?

1. 50 ml of milk at 25 degrees C in a trough of water at 50 degrees C.
2. 50 ml of milk at 50 degrees C in a trough of water at 25 degrees C.
3. 40 ml of milk at 50 degrees C in a trough of water at 25 degrees C.
4. 40 ml of milk at 25 degrees C in a trough of water at 50 degrees C.

The given answer is (1), but why not (4)? Is it because (1) has a greater volume of milk? Pls help. I’m kind of muddled.

[ADoc]

tianzhu:

wkong:

Thanks ADoc for the explanation of the questions I posted earlier on.


I have another question that I need advice:

The answer is (3) or (4)?


http://postimage.org/image/1sz47y62s/

Hi

I cannot remember seeing term like magnetic energy in PSLE science under the topic of Energy.

The forms of energy are Potential, Kinetic, Heat, Light, Sound and Electricity.

Best wishes

Hi tianzhu! You're absolutely right about the 6 forms of energy that the primary curriculum is required to impart.

There are some schools that do teach other forms of energy such as tidal, wind, mechanical, even nuclear. Their teaching is skewed towards that most forms of energy can be traced to a single source. In addition, students are taught that energy classificatons are mere (human) categorisations and are usually subsets of each other to be precise. The concept that energy is the ability to do work or that energy is required to make things move or do work is especially emphasised. This concept is really a powerful one such that it tinkles the student's mind that as long as something moves, there must be at least one energy involved.

Having said these, I am not sure of the setter's intention and the origin of the question. If the intention is to (1) identify the order of enegy conversion, (2) identify the 6 forms of energy that are \"taught\", then the answer is obvious. Else this question will be finding its place in the sacred basket of ambiguous & contentious questions. haha!

By the way, I totally for \"primary questions use primary knowledge & syllabus\". That's only fair for the kids. The onus lies with the setter to ensure that the options for answers must be within primary syllabus as well. If not, it will just invite fires.

Hi KWong, what's your kid's teacher's \"answer\" and explanation? tks!

cheers!

[ADoc]

anneshirleygilbert:

Need some help for this question on heat:


In which of the following will the milk gain the most amount of heat?

1. 50 ml of milk at 25 degrees C in a trough of water at 50 degrees C.
2. 50 ml of milk at 50 degrees C in a trough of water at 25 degrees C.
3. 40 ml of milk at 50 degrees C in a trough of water at 25 degrees C.
4. 40 ml of milk at 25 degrees C in a trough of water at 50 degrees C.

The given answer is (1), but why not (4)? Is it because (1) has a greater volume of milk? Pls help. I'm kind of muddled.

Hi there!
I agree ans should be (1). For the same temperature difference, the greater the amount of a substance (volume or mass), the more energy it will (have to) gain in order to be raised by the same amount of temperature.

In our usual daily experience, imagine having two cups of hot kopi (aka trough) with an ice cube (aka milk) and another ice cube double the size. Which cup of kopi will be colder (aka lose more heat to milk, in other words milk gain more heat)?

Experience tells us that the kopi with the bigger ice cube would be colder. Drawing similarity: bigger ice cube = larger volume of milk; colder kopi = greater heat loss which means greater heat gain by the larger volume of milk.

In secondary physics, this concept is explained via heat capacity.

Hope this kopi experience will be useful to you when explaining to your kid.

[ChiefKiasu]

ADoc:

anneshirleygilbert:

Need some help for this question on heat:


In which of the following will the milk gain the most amount of heat?

1. 50 ml of milk at 25 degrees C in a trough of water at 50 degrees C.
2. 50 ml of milk at 50 degrees C in a trough of water at 25 degrees C.
3. 40 ml of milk at 50 degrees C in a trough of water at 25 degrees C.
4. 40 ml of milk at 25 degrees C in a trough of water at 50 degrees C.

The given answer is (1), but why not (4)? Is it because (1) has a greater volume of milk? Pls help. I'm kind of muddled.

Hi there!
I agree ans should be (1). For the same temperature difference, the greater the amount of a substance (volume or mass), the more energy it will (have to) gain in order to be raised by the same amount of temperature.

In our usual daily experience, imagine having two cups of hot kopi (aka trough) with an ice cube (aka milk) and another ice cube double the size. Which cup of kopi will be colder (aka lose more heat to milk, in other words milk gain more heat)?

Experience tells us that the kopi with the bigger ice cube would be colder. Drawing similarity: bigger ice cube = larger volume of milk; colder kopi = greater heat loss which means greater heat gain by the larger volume of milk.

In secondary physics, this concept is explained via heat capacity.

Hope this kopi experience will be useful to you when explaining to your kid.

Great answer. How about repurposing the same question in the following forms:
a. In which of the following will the milk experience the greatest temperature change? Ans: All of the above

b. In which of the following will the milk take the longest time to reach the temperature of the trough of water? Ans: (1) and (2)

[tianzhu]

wkong:

This question is abit tricky, should it be (2) or (3)? Which is the keyword that gives the hint of the answer?



http://postimage.org/image/w313pnlw/

Hi wkong

Good Morning.

I think we are advised to refrain from using the term “insulator of heat’ in PSLE science. If I remember correctly, there are some discussions in earlier posts.The term to use is 'poor conductor of heat'.

So, I would not consider (2)

(1) is out as copper is non magnetic.
(4) is out as well.

There only choice left is (3).

Best wishes

[atutor2001]

ChiefKiasu:

Great answer. How about repurposing the same question in the following forms:
a. In which of the following will the milk experience the greatest temperature change? Ans: All of the above

b. In which of the following will the milk take the longest time to reach the temperature of the trough of water? Ans: (1) and (2)

Wow Chief, don't be so cruel leh. The original question is already tough enough and you have up the level of complexity. :lol:

Can help to explain your answers? Thanks

[wkong]

tianzhu:

wkong:

This question is abit tricky, should it be (2) or (3)? Which is the keyword that gives the hint of the answer?



http://postimage.org/image/w313pnlw/

Hi wkong

Good Morning.

I think we are advised to refrain from using the term “insulator of heat’ in PSLE science. If I remember correctly, there are some discussions in earlier posts.The term to use is 'poor conductor of heat'.

So, I would not consider (2)

(1) is out as copper is non magnetic.
(4) is out as well.

There only choice left is (3).

Best wishes

Thanks for the explanation Tianzhu.

[ADoc]

atutor2001:

ChiefKiasu:

Great answer. How about repurposing the same question in the following forms:
a. In which of the following will the milk experience the greatest temperature change? Ans: All of the above

b. In which of the following will the milk take the longest time to reach the temperature of the trough of water? Ans: (1) and (2)

Wow Chief, don't be so cruel leh. The original question is already tough enough and you have up the level of complexity. :lol:

Can help to explain your answers? Thanks

love these questions!
All things being equal, especially with the assumption that the trough of water remains at constant temperature (i.e. keeps supplying or absorbing heat constantly without changing it's temperature); yes, I totally agree with Chief's answers.

(a) within the primary curriculum's concept that heat transfer will cease until the objects attain the same temperature, all the 4 options will experience the greatest (identical) temperature change since the temperature difference is the same (+/- 25 deg). Tricky question! :lol:

(b) again, to increase or decrease to the temperature (difference of 25 deg) of the trough, a greater amount of the same object has to lose or gain more heat in order achieve an identical increase or decrease in temperature. Just like a boiling a teaspoon of water and a mug-full of water respectively: it will take a longer time to heat up the latter.

In other words: greater mass or volume ---> more heat required to raise its temperature ---> more (longer) time needed

cheers!

[anneshirleygilbert]

My word!!! Won’t my daughter get a fit when she comes home from school to read the answers!!! She and I thought that was a simple question needing a simple answer for our muddled minds, but you have widened the scope so extensively. Thanks a bunch, ADoc and ChiefKiasu. Your answers are very thought-provoking. Thanks again.