Q&A - PSLE Science

[ChiefKiasu]

tianzhu:

...Part (b) --- Without any doubts, Gear Y will turn more rounds as its diameter is smaller than Gear Z.But, how many more?Could we tell based on the information given in the question?

...

Yes we can, by counting the number of spokes on the gears.
Gear Y = 10
Gear Z = 16
Ratio = 16:10 => if Gear Z turns 1 round, Gear Y would have turned 1.6 rounds.

So if Gear Z turns 5 rounds, Gear Y would have turned 5x1.6=8 rounds.

[tianzhu]

Thank you for your help.


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[Drdj]

[Moderator's note: Topics merged.]


http://www.postimage.org/image.php?v=Pq12Ooo0

Hi, can you help me explain why the given answer is option (4)?
Thanks.

[tianzhu]

Drdj:

[Moderator's note: Topics merged.]


http://www.postimage.org/image.php?v=Pq12Ooo0

Hi, can you help me explain why the given answer is option (4)?
Thanks.

Hi
Let us recap

In PSLE science, students are not taught how to determine the polarity of an electromagnet. They learned that an electromagnet is made when you coil an electric wire a few times around a magnetic material.
Copper is a non magnetic material.(MPH PSLE Science Guide pg 64)
For magnets, like poles attract and unlike poles repel. (MPH PSLE Science Guide pg 66)

Consider (1) --- The bulb lights up as a closed circuit is formed. The magnet may move to the left if unlike poles are facing one another.
(1)is a logical answer.

Consider(2) ---The copper remains in the same position as it is non magnetic. The magnet may move to the right if like poles are facing one another.Hence (2) is also correct.

Consider (3) ---The magnet either moves to the left or right.B and C cannot happen at the same time.Therefore (3) is out.

Consider(4) ---For the same reason as (3), this option is also out.

Therfore option (1) and (2) are logical.Where is this question from?

[Drdj]

It's from Tao Nan SA1 2008 paper.

Thanks for your quick response

[Drdj]

It's from Tao Nan SA1 2008 paper.

Thanks for the quick response

tianzhu:

Drdj:

[Moderator's note: Topics merged.]

http://www.postimage.org/image.php?v=Pq12Ooo0

Hi, can you help me explain why the given answer is option (4)?
Thanks.

Hi
Let us recap

In PSLE science, students are not taught how to determine the polarity of an electromagnet. They learned that an electromagnet is made when you coil an electric wire a few times around a magnetic material.
Copper is a non magnetic material.(MPH PSLE Science Guide pg 64)
For magnets, like poles attract and unlike poles repel. (MPH PSLE Science Guide pg 66)

Consider (1) --- The bulb lights up as a closed circuit is formed. The magnet may move to the left if unlike poles are facing one another.
(1)is a logical answer.

Consider(2) ---The copper remains in the same position as it is non magnetic. The magnet may move to the right if like poles are facing one another.Hence (2) is also correct.

Consider (3) ---The magnet either moves to the left or right.B and C cannot happen at the same time.Therefore (3) is out.

Consider(4) ---For the same reason as (3), this option is also out.

Therfore option (1) and (2) are logical.Where is this question from?

[tianzhu]

Thank you for your help.


Why does the temperature not rise until all the ice melted into water? Where does the energy for melting the ice come from?

I did a search using Google/Yahoo and came across an interesting article.
http://www.scientificpsychic.com/mind/colddrink1.html

There is latent (hidden) heat of fusion during the melting of ice when the temperature remains at 0 degree Celsius.

[tianzhu]

Going back to Drdj"s question.


Hi, sorry for leading you to the wrong path earlier.

From MPH PSLE Guide (pg 148), for a bulb to light up, the metal tip and metal casing of a bulb must be connected to different poles of the battery.

In this question, the connections are only at the metal casings; hence the light will not light up. Hence option (1) is out.

Therefore, option (2) is correct.

Life is indeed interesting for our 12 years old kids, have to be very observant when doing Science questions

[Dharma]

tianzhu:

Going back to Drdj\"s question.


Hi, sorry for leading you to the wrong path earlier.

From MPH PSLE Guide (pg 148), for a bulb to light up, the metal tip and metal casing of a bulb must be connected to different poles of the battery.

In this question, the connections are only at the metal casings; hence the light will not light up. Hence option (1) is out.

Therefore, option (2) is correct.

Life is indeed interesting for our 12 years old kids, have to be very observant when doing Science questions

Hi Tianzhu,

The likely observations are ...

A - the bulbs will not light up ...your reasoning is correct. This is not a likely observation.
B & C - if end of the electromagnet facing the magnet and the magnet are like poles, the magnet will move to the right...Magnetic force of repulsion. If the end of the electromagnet facing the magnet and the magnet are unlike poles, the magnet will move to the left ...Magnetic force of attraction....Therefore B and C are likely observations.

D - Copper is a non-magnetic material ...it will remain at the same position.

I will go for (4) - B,C and D only

[Dharma]

tianzhu:

Energy


Thank you for your help.

Based on the information in the question, can we tell how high the rubber ball will reach after bouncing off the concrete surface?
(2) or (3) or anywhere between(2) and (3) are logical answers.Some of the KE has been converted into heat and sound energy, hence the ball will not rebound to its original position.

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Hi Tianzhu,

I don't think it is possible to accurately predict the exact position the ball will bounce back after hitting the concrete surface....for me ...somewhere midway between Point 1 and Point 2 up to Point 3 will be reasonable....although I think it is likely to be closer to Point 2....as concrete is hard and this will enable the ball to bounce back high ...but definately not to Point 1.