Q&A - PSLE Science

[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.

http://farm4.static.flickr.com/3638/3552206045_f1f6136f0b_o.jpg\">

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.

[tianzhu]

Dharma:

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

Hi Dharma

Yes, B and C are likely observations, but they do not occur at the same time.

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.

[Dharmaratnam]

tianzhu:

Dharma:

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

Hi Dharma

Yes, B and C are likely observations, but they do not occur at the same time.

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.

Hi Tianzhu,

Maybe if \"all possible observations\" is used in the qn then ...will be clearer.

[Drdj]

[Moderator's note: Topics merged.]


http://www.postimage.org/image.php?v=Pq1EkKm0

Hi there, I have another query on this question - it's from the PSLE 5 year series ...
The answer given is distance y will decrease.
Iron ring will be attracted to magnet , but gravitational force exerted by combined weight of the iron ring and magnet A is greater than that of magnet A alone, reducing the distance y.

My question is : How do you know the gravitationl force is greater than the magnetic force of repulsion (which causes distance y in the first place?)

Thanks in advance.

[jedamum]

discuss psle science http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=1727&start=0.

pls do a search before starting a thread.
TQ

[Drdj]

jedamum:

discuss psle science http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=1727&start=0.

pls do a search before starting a thread.
TQ

My apologies. I was at Pg 12 of the link you mentioned, but i clicked on 'New Post' instead - this seems to be the incorrect option - I should probably click 'Quote' to any of the posts. Sorry about that.

[jedamum]

Drdj:

but i clicked on 'New Post' instead - this seems to be the incorrect option - I should probably click 'Quote' to any of the posts. Sorry about that.

seems like a lot of newbie make this type of mistake. must be too excited/anxious...

[tianzhu]

Hi


To avoid starting a new thread, you have to hit post reply.This will keep you in the existing thread.

From MPH PSLE Science Guide pg 194/195

Weight is the amount of gravitational force acting on an object. It tells us how heavy an object is.
There are two types of magnetic forces — attraction and repulsion.

In this question, the force of repulsion is in action. It keeps the two magnets at a distance y from one another at the beginning stage. Iron is magnetic and will be attracted to magnet A. The combined forces of the magnet A and the piece of iron ring will reduce the distance y.

To see it in another way, imagine the distance y being replaced by a spring. The two magnets are replaced by two pieces of non magnetic materials such as plastic A and B. You put an additional weight on top of A. Will the spring be compressed as compared to its initial position?