Q&A - PSLE Science
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chrisu:
Yes, you are absolutely correct that the current won't be large if we use battery as battery has internal resistance.Not forgetting a battery will have internal resistance and this will vary between a new and used battery. A used battery will have higher internal resistance if I didn't remember wrongly.
Thus the current may not be too high if the battery is shorted.
The electrical source that I was having in mind was a DC transformer where a potential difference of 3V can be maintained. However, personally, I still find it hard to believe that a mere 3V potential difference will melt a wire but the computed current of 3000 amp is indeed very large and should be able to melt it (compared to the current needed for our normal household appliances which is less than 13 amp r.m.s) -
Hi atutor2001,
You are right to point out the short circuit part and the high current in the circuit. That's why it is important to incorporate a fuse in the appliances or circuit or device where it will open the circuit to prevent further damages to the components.
The teacher should not use short circuit to teach the difference between closed and open circuit. There is a great difference between short and closed circuit. Short circuit is to be avoided and the danger of it should not be disregarded. So even for primary school, the teacher should not confuse the students with short circuit and closed circuit.atutor2001:
Yes, you are absolutely correct that the current won't be large if we use battery as battery has internal resistance.chrisu:
Not forgetting a battery will have internal resistance and this will vary between a new and used battery. A used battery will have higher internal resistance if I didn't remember wrongly.
Thus the current may not be too high if the battery is shorted.
The electrical source that I was having in mind was a DC transformer where a potential difference of 3V can be maintained. However, personally, I still find it hard to believe that a mere 3V potential difference will melt a wire but the computed current of 3000 amp is indeed very large and should be able to melt it (compared to the current needed for our normal household appliances which is less than 13 amp r.m.s) -
A mountainer climbing to higher altitudes finds it difficult to breathe, as there is ----
a) less air b) less nitrogen c) more carbondioxide d) less water vapour
My answer is a) as density if air is less at higher altitudes whereas oxygen requirement by body remains the same.
But given answer is d) less water vapour. Reason being, composition of gases in atmosphere remains fairly constant at all altitudes. It is only the amount of water vapour that differs.
Can anyone help? -
tinasen:
Is this taken from past yr paper or revision bk?A mountainer climbing to higher altitudes finds it difficult to breathe, as there is ----
a) less air b) less nitrogen c) more carbondioxide d) less water vapour
My answer is a) as density if air is less at higher altitudes whereas oxygen requirement by body remains the same.
But given answer is d) less water vapour. Reason being, composition of gases in atmosphere remains fairly constant at all altitudes. It is only the amount of water vapour that differs.
Can anyone help?
The answer shd be air. AT high altitude, the air pressure is lower, so the same volume of air will have less oxygen in it since the oxygen molecules (and also the rest of the gases) are packed less closely. -
From a revision book.
I also think the correct answer is a)
Thanks Nebbermind. -
for science, it’s always better to stick to the one the school prescribed. The qns in some of the easily available revision bks can be very confusing…not a good thing to attempt when so close to the PSLE.
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Pls help me.
Is ceramic man-made? -
Ceramic is man made.
It may be made from clay (natural material) but it is man made -
Sun_2010:
thank you Sun_2010!.Ceramic is man made.
It may be made from clay (natural material) but it is man made -
i have a qn.
Is it correct to say that the stress ball can be compressed?Explain ur answer.
pls help me answer the qn.thank you.
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