Q&A - PSLE Science

[Eddow]

tisha:

tisha:

http://postimage.org/image/21pr64bo/



Need help with this Q from Catholic High SA1 2010 Science paper.

BTW, the answer key says the answer is (4). But DS and DH argue that the answer is (3). I'm a blur queen when it comes to science. :lol:

DS1 said ans is (3) too. Additional info.. mass x distance = amt of gravatational potential energy.

[jesschan]

atutor2001:

From the graph, the teacher's interpretation is wrong. The brightness become zero at the 7th battery, not the 6th battery.

This teacher must be thinking that the bulb becomes very bright at the 6th battery then fuses and drop to zero. If that is the case, then there should be a vertical line dropping down at the 6th battery and not a \"sloping\" line dropping from 6th to 7th battery.

Well, what to do, the teacher teaches without much thought.

Thanks atutor and nebbermind for the comments. Just wondering if the x-axis is time or voltage, will there will any difference in the answer?

[wkong]

jesschan:

atutor2001:

[quote=\"jesschan\"]Thanks, wkong. But my son had the same answer and was marked wrong.... I wonder what is wrong with the answer....

Is the word \"brightest\" in your son's answer? Maybe that is the keyword they are looking for. Science marking scheme can be quite silly at times, especially in school.

Yeah, he did. But his teacher said that the bulb fuses at the 6th battery?!! :? And he lost 2 marks for the this, not knowing why....[/quote]Hmm.. guess my DS's answer is not correct since your DS also got it wrong.

I checked with the sch teacher and here is what he explained:

Based on what I see from the attached graph, there may be an error in the presentation. It is not possible for the bulb to dim from the 6th battery and then come to nothing at the 7th battery. The graph should show a drop immediately at the 6th battery to zero.

The reason I would like to offer is that the amount of energy provided by the total 6 batteries used is too great so that the bulb fuses. Hence, there should be an open circuit immediately and the graph should register a sudden drop at the 6th battery.

Hopes that helps.

[tisha]

Eddow:

tisha:

[quote=\"tisha\"]http://postimage.org/image/21pr64bo/



Need help with this Q from Catholic High SA1 2010 Science paper.

BTW, the answer key says the answer is (4). But DS and DH argue that the answer is (3). I'm a blur queen when it comes to science. :lol:

DS1 said ans is (3) too. Additional info.. mass x distance = amt of gravatational potential energy.[/quote]Thanks Eddow. Without the additional info is it possible to answer this Q. BTW is the formula mass x distance = amt of gravatational potential energy taught in primary school science.

[jesschan]

wkong:

I checked with the sch teacher and here is what he explained:

Based on what I see from the attached graph, there may be an error in the presentation. It is not possible for the bulb to dim from the 6th battery and then come to nothing at the 7th battery. The graph should show a drop immediately at the 6th battery to zero.

The reason I would like to offer is that the amount of energy provided by the total 6 batteries used is too great so that the bulb fuses. Hence, there should be an open circuit immediately and the graph should register a sudden drop at the 6th battery.

Hopes that helps.

I have been pondering over this question and I think maybe the bulb did fused at the 6th battery. By the time the 7th battery was added, the bulb had already fused.

[CoffeeCat]

jesschan:

wkong:

I checked with the sch teacher and here is what he explained:

Based on what I see from the attached graph, there may be an error in the presentation. It is not possible for the bulb to dim from the 6th battery and then come to nothing at the 7th battery. The graph should show a drop immediately at the 6th battery to zero.

The reason I would like to offer is that the amount of energy provided by the total 6 batteries used is too great so that the bulb fuses. Hence, there should be an open circuit immediately and the graph should register a sudden drop at the 6th battery.

Hopes that helps.

I have been pondering over this question and I think maybe the bulb did fused at the 6th battery. By the time the 7th battery was added, the bulb had already fused.

I agreed with Nebbermind about the graph thingy.
When one plots the graph, after the 6th battery is added, the brightness reached its peak and hence that brightness value was plotted. It is only when the 7th battery is added and the bulb fuses (it will take only a fraction for the bulb to fuse) then a brightness of 0 is plotted.
Finally because this is a line graph, the various dots are joined by a straight line, hence the confusion regarding the steeping line. The steep line doesn't mean anything.

[starlight1968sg]

Anybody doing P6 Young Scientist Card (IT whiz)?

Please pm me.
Many thanks.

[atutor2001]

Misconception on graph plotting :


Many think that :
\"For every value of x coordinate (e.g. number of batteries) there can only be one value for the y coordinate (e.g. brightness)\"

No, there is no such restriction - for each x coordinate, there can be more than 1 value for the y coordinate.

For example, if the bulb becomes very bright then fused at the 6th battery, there will be 2 values of y (brightness) for the \"6th battery\".

The 1st value is the maximum brightness and the 2nd value is zero brightness. Since the maximum brightness occurred first, the graph from the coordinates of the 5th battery will be joined to the point of maximum brightness then vertically downwards to the zero brightness, then to the 7th battery along the zero line.

[atutor2001]

jesschan:

Thanks atutor and nebbermind for the comments. Just wondering if the x-axis is time or voltage, will there will any difference in the answer?

When a bulb fused, the action is immediate / instantaneous i.e. a drop from maximum brightness to zero in almost zero duration or voltage change. Therefore, the answer should not be any different if the x-axis is changed to voltage or time.

[jesschan]

Thanks, atutor. So do u also agree that the bulb could have fused at the 6th battery?