Physics : Lissajous Figures

Ever since I first read of them in junior college, I have always found Lissajous figures mesmerizing and beautiful.
I found a simple way to create them without using two function generators (poor me; I could only afford one) by using the left and right audio channels of a laptop.

You can also create them in sand! This is a hands-on experiment I did at a science camp; needless to say, the kids loved messing around with it.

Physics : Corner cube reflectors

This is a corner reflector used by surveyors to measure distances precisely by bouncing lasers off them. [Link to Wikipedia article]. Read up on how they work; their operation is relevant to total internal reflection and prisms in O&A-level physics.

This particular reflector was near bar named "The Colonial" above Little India Station on the underground NEL line. They can also be found on almost all the pillars that support the elevated sections of old East-west and North-south MRT lines.

The coolest thing about these reflectors is that the Apollo astronauts left a panel of them on the moon. [Link to Wikipedia Article] I really think it is ridiculous that anyone should doubt that men have been to the moon, especially when observatories around the world bounce lasers off those reflectors to measure the distance to the moon. Don't try using your laser pointers; the power needed to reach the moon is in the neighbourhood of a hundred watts, and even then, only a few photons get reflected by the corner reflectors and make it back to earth!

Chemistry : Air conditioner refrigerant fluids

This is a photograph of a tank of refrigerant fluid used by a repairman to recharge old air conditioners and refrigerators.

The liquified gas in the tank is Chlorodifluoromethane [Link to wikipedia article] which is a formed by allowing chlorine and fluorine atoms to replace hydrogen atoms in the methane molecule in a textbook reaction known as substitution.

GP Essay : The language of mathematics is the perfect language. Do you agree?

This essay topic is not an easy one to write on.
A student of mine posed this topic to me as a friendly challenge which I was glad to take on.
I might not have done as great a job on this as I would have liked but this represents my best efforts.
I was not time constrained; I took about 4 hours to write this in two sittings.

Click here for the essay:
The language of mathematics is the perfect language. Do you agree?

Physics : Trebuchet

Built this trebuchet in 2009 in preparation of a science camp. Didn't get to use it, but still hope to do so in a camp sometime soon. Test fired it; needs refinements on the release mechanism.

Great demo for conversion of energy. Definitely quite fun to setup and fire. Use tennis balls as ammo, but ideally something heavier should be swung on this although safety concerns would kick in. I think water bombs make a good ammo too.

Physics : Chladni Patterns

Chladni patterns are a really cool way to visualize standing waves.

For more info on the man and the field he helped pioneer:
Ernst Chladni on Wikipedia
Cymatics on Wikipedia

I rigged a speaker to an amplifier and a frequency generator. The speaker was modified such that the cone directly drives a square metal plate. Yellow art sand was added and when certain frequencies were dialed into the frequency generator, the sand would quickly coalesce to form patterns.

More details on setup will be posted here. I'm still working on it at the moment.

Meanwhile, enjoy the pictures!

GP Essay : Music has one purpose – to entertain

I wrote this GP essay some time ago for one of my students.

Makes for an interesting read; not the regular current affair GP essay question.

Click here for the essay:

'Music has one purpose – to entertain' Using specific examples, consider this view.

Chem : Table of the Solubility of Ionic salts

Solubility List

Exceptions

All Sodium Salts are soluble

All Potassium Salts are soluble

All Amonnium are soluble

All Nitrates are soluble

These exceptions over-ride the solubility table below. A useful way of remembering this is to recall the word SPAN.

Solubility Table

	Soluble	Insoluble
Sulphates	All soluble except	Barium, Lead, Calcium, Silver, Mercury
Hydroxides	Barium and calcium slightly soluble	All other hydroxides insoluble
Carbonates		All insoluble
Chlorides	All soluble except	Silver, Lead, Mercury

Chem : Metal Reactivity list

'O' level Chem Metal Reactivity list with Hydrogen and Carbon.

Metal Reactivity list
Common Name	Symbol	Illustrative examples
Potassium
Sodium
Calcium
Magnesium		Burning Mg underwater
Aluminum		Aluminum Pots. Thermite. Napoleon III VIP Dinnerware
Carbon		The Blast Furnace
Zinc		Galvanized Roofing
Iron
Tin		The tin can
Lead		Plumbum
Hydrogen
Copper
Silver		Tarnish
Gold		Aqua Regis

Chem : Cation and Anion List

This is a list of cations and anions commonly encountered in 'O' Level Chemistry.

Common Cations

Name	Formula
Aluminum	Al+3
Ammonium	NH4+
Barium	Ba+2
Calcium	Ca+2
Copper(I)	Cu+
Copper(II)	Cu+2
Iron(II)	Fe+2
Iron(III)	Fe+3
Hydrogen	H+
Lead(II)	Pb+2
Magnesium	Mg+2
Potassium	K+
Silver	Ag+
Sodium	Na+
Zinc	Zn+2

Common Anions

Simple ions:
Fluoride	F-
Chloride	Cl-
Bromide	Br-
Iodide	I-
Oxide	O2-
Sulfide	S2-
Hydroxide	OH-
Phosphate	PO43-
Sulfate	SO42-
Nitrate	NO3-
Carbonate	CO32-
Dichromate	Cr2O72-
Permanganate	MnO4-

Q : Why the name Cations?

A : These ions are Positive in charge, and gather at the Cathode during electrolysis.

Q : Why the name Anions?

A : These ions are Negative in charge, and gather at the Anode during electrolysis.