Q&A - PSLE Science

[starlight1968sg]

We know salt lowers the melting point of ice and increases the boiling point of water.

Why do people in winter put salt on the snow?
Thanks.

[tianzhu]

starlight1968sg:

We know salt lowers the melting point of ice and increases the boiling point of water.

Why do people in winter put salt on the snow?
Thanks.

Hi starlight1968sg

Good Morning.

You may find this link helpful.
http://www.sciencekids.co.nz/videos/chemistry/icesnow.html

Best wishes

[Belle2011]

Dear all,

We know that magnetism can pass through non-magnetic materials. Can magnetism pass through magnetic materials? Can give an example to illustrate?
Thank-you.

Cheers,
Belle.

[tianzhu]

Belle2011:

Dear all,

We know that magnetism can pass through non-magnetic materials. Can magnetism pass through magnetic materials? Can give an example to illustrate?
Thank-you.

Cheers,
Belle.

Hi Belle

Good Morning.

In primary science, students learned that magnetic force can pass through thin sheets of non magnetic materials such as paper, glass or wood.

However if the magnetic force is too weak or the material is too thick, magnetic force may not be able to pass through.

Best wishes

[Belle2011]

tianzhu:

Hi Belle


Good Morning.

In primary science, students learned that magnetic force can pass through thin sheets of non magnetic materials such as paper, glass or wood.

However if the magnetic force is too weak or the material is too thick, magnetic force may not be able to pass through.

Best wishes

Dear tianzhu,
Thanks for reply.
May I find out if magnetism can pass through magnetic materials? Can you give an example to show it?

Cheers,
Belle.

[Nebbermind]

perhaps this can help.


http://www.coolmagnetman.com/magshield.htm

[atutor2001]

Belle2011:

May I find out if magnetism can pass through magnetic materials? Can you give an example to show it?

I guess you must have read somewhere that magnetism pass through ALL materials (including magnetic material), which is actually correct.

The problem lies with the definition of \"pass through\".

In primary school, \"pass through\" is defined as going in from one side and coming out directly from the opposite side, using the shortest path.

In scientific definition, \"pass through\" means going into the magnetic material, using whatever path that the magnetic force would like to travel inside the magnetic material, and then coming out of the magnetic material. Therefore, the more accurate definition is

\"Magnetic material will redirect magnet force.\"

If a steel sheet is placed in front of a magnet, magnetic force prefers to travel through the steel sheet than through air. As a result, it will take the longest path available inside the steel sheet and comes out of the sheet at the edges. As a result, any object placed directly on the opposite side of the steel sheet will not experience any magnetic force as the force would not come out through the \"broad surface\" but through the edges.

[Belle2011]

atutor2001:

I guess you must have read somewhere that magnetism pass through ALL materials (including magnetic material), which is actually correct.

This is the tricky part; in school nothing much was mentioned and we have a feeling that magnetism can't pass through magnetic materials.
But when you put a magnet near an iron nail, this iron nail can in turn attracts some iron filings or paper clips which means the magnetism has passed from the magnet to the iron nail.
I am getting more and more confused.
Cheers,
Belle.

[tianzhu]

Belle2011:

May I find out if magnetism can pass through magnetic materials?

Belle2011:

This is the tricky part; in school nothing much was mentioned and we have a feeling that magnetism can't pass through magnetic materials.
But when you put a magnet near an iron nail, this iron nail can in turn attracts some iron filings or paper clips which means the magnetism has passed from the magnet to the iron nail.
I am getting more and more confused.

Hi

In PSLE science, students learned that magnetic force cannot pass through magnetic materials.

What you’ve described is an example of magnetism by induction. The iron nail is magnetised by induction.

Best wishes

[atutor2001]

tianzhu:

What you’ve described is an example of magnetism by induction. The iron nail is magnetised by induction.

Best wishes

Magnetic induction is the result of magnetic force passing through the iron nail (a magnetic material). I have copied this write-up from the internet :

\"As an iron nail is brought close to a bar magnet, some flux lines emanating from the north pole of the magnet pass through the iron nail in completing their magnetic path. Since magnetic lines of force travel inside a magnet from the south pole to the north pole, the nail will be magnetized in such a polarity that its south pole will be adjacent to the north pole of the bar magnet. There is now an attraction between the two magnets.\"

For those interested, you may visit this site
http://www.tpub.com/neets/book1/chapter1/1i.htm

In my opinion, it is important to teach our kids the truth and also to accept the limitation of the primary science syllabus - recognising the difference in definitions of the words used.