Thursday, May 29, 2008

10:31 PM

NUS Physics Enrichment "Camp" Day 1

Post completion: 31 May 2008 12pm

Today was the start of the two-day Physics course at NUS. It was supposed to for J1 students but NYJC quite extra lah, 14 J2s and 1 J1 went. This is not a camp as the name suggests. It lasted so long that it made me so tired and left me with no time to blog when I reached home.

The first part of the day was about lectures given by four professors.

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Introduction to Nanoworld. The most interesting of all!

The first step before you enter the nanoworld is to appreciate what is one nanometer.

An analogy he gave was about the the human hair. Take a normal human hair which was about 100 micrometers. Chop into 100 slices, take one slice and chop into another 100 slices. The diameter of this slice is about 1 nanometre (10^-9 m)

He explained that atoms behaved differently in a nanoworld (microscopic) as compared to the macroscopic world we live in.

The most obvious would be colour. Colour is due to photons of a certain frequency begin given out by an atom. This is caused by an "excited" electron dropping from a high energy level to a lower one. Of course, before it was "excited", it gained energy from an external source (like electricity) before dropping after a certain interval. (See Quantum 2 notes)

In a nanoworld, the space given to the atom is so small, the electron does not move to the same high energy level as it can previously. Subsequently, the "fall" it experiences later is not so great so the photon it releases will be of a lower frequency.

Tangible proof! Gold appears as yellowish under normal conditions. In the nanoworld, it appears as red. This is shown by the above bottle which contains 50nm gold particles immersed in water. Red appears due to the smaller space the gold electrons can move. Red has lower frequency than yellow, in fact it is the colour with the longest wavelength in the visible spectrum.

Scanning Tunneling Microscope. See Quantum 3 notes page 11.

Still got other equipment like SEMs and TEMS. But lazy to explain.

The origin of the concept of nanotechnology came from American physicist Richard Feynman. He publicised his idea in a 1959 speech "There's Plenty of room at the Bottom". Obviously, someone had to start the ball rolling and he was the guy.

He demonstrated a live experiment with two volunteers. He asked them to hammer a normal ice block and another with toilet paper frozen in it. The second block could not be smashed no matter how many times they tried. The toilet paper was acting like a "crack stopper" preventing any crack from extending through the entire height of the block.

Materials which are scratchproof and are water-resistant are desired especially in the car industry. Using nanotechnology, atoms can be manipulated to mimic this structure. Thus materials which are high/light and have high hydophobicity can me made.

One of the early applications of nanotechnogy was by Intel. Ever since 1970s, it has developed and incorporated nano-technology into its industrial processes so chips of increasing power can be made over the decades. The trend of the number of transistors doubling in a single chip (or die in wafer-fabrication) every 1.5-2 years was observed by Intel's co-founder Gordon Moore. His Moore's law was then coined to describe this trend

(My addition)
The Intel's 286 processor in 1982 had approximately 100 000 transistors. Fast-forward almost 26 years to late 2007. The quad-core Core 2 Extreme (Yorkfield XE) had 820 million transistors. Do the maths, doesn't this seem to fit his law perfectly? All these can only be made possible through nanotechnology.

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Stars and galaxies.

Many of the concepts were too chim for me to comprehend despite my interest. So I'll just speed through it.

Life cycle of stars, read it if you can.

The formula on the right is unfamiliar but can roughly derive it.

Dunno what the hell is this lah.

One useful thing I got out of it was the concept of hydrostatic equilibrium in stars and planets. Simple, its an equilibrium between gravity and pressure. When something is done to upset the equilibrium, it will attempt to self-correct. For eg, if gravity tries to pull its atmosphere of gas/plasma down, the smaller volume will result in a higher pressure pushing the gas/plasma back up. The problem arises if it does not self-correct in time, the atmosphere may collapse into a black hole or implode into a supernova.

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Physics in daily life.

This was quite boring as we already knew most of the stuff. Things like stacking chairs in circuses, pulling cloth under cups and cutlery and Air cushion used by firemen. The only thing I'm not sure off was the Anti-locking breaking system (ABS).

I know how it works, but the question he posed on which two wheels it has to be installed into stumped many. He said to install on the back wheel so the back wheels can be unlocked in the event of skidding, reason being the static friction of the rolling back wheels is greater than the kinetic friction of the sliding locked front wheels. Do a bit of visualisation, and you know why the car should not spin.

I though it should the front wheels? My reason is that the steering control of the front wheels should be maintained if one wishes to avoid an accident. If the front wheel locks up, the driver essentially loses the ability to recover from a spin when it starts. The ABS system should then kick in to unlock the front wheels.

Anybody can provide some inspiration? An Internet search yielded no results.

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1. First hands-on experiment of the day dealt with atomic spectra.

We were supposed to use a spectrometer to determine the identity of an unknown element based on its emission line spectrum. Samples of hydrogen and mercury were given for us to experiment too.

Does this look familiar? See Quantum 2 notes page 7. (This image has been adjusted by me as the orginal was very dark).

The blueish light was from an electrified tube of "excited" Mercury vapour. The slit nearest to the tube is a slit of variable width. The lens helps to focus the light to a diffraction grating which splits the light into the component colours. The light sensor can then be rotated (notice the protractor?) to detect the colors. The type of color and the angle from the centre is then noted by a computer.

Emission lines of mercury presented as a graphical diffraction pattern.

Hydrogen glows an eerie purple.

First order of unknown element DT-018 viewed through a diffraction grating. (Suspect this is Neon)

Random viewing of conventional sources through the grating.

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2. Measure the wavelength of laser.

Superposition topic revisited.

The green laser output from an industrial-type machine is shown through a 80-line diffraction grating. Look at how many orders of maxima are there! The red laser was from another group. We experimented with 300 and 600-line gratings.

The entire setup. We had to wear those nerdish looking red goggles for protection.

This was what we had to do as Yanyu and Yingyu demonstrates. (Of course this was a sneak photo!) Measure the distance between the corresponding orders with a measuring tape. With the distance between the grating and the screen also obtained in the same manner, we can calculate the wavelength.

The red laser does not seem as powerful as the green one.

My personal green laser seems more powerful those setups lah! Lol, look at the intensity! (This image has not been adjusted)

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3. Magnetic force on current-carrying conductor

A wire loop connected to a DC power source was suspended above some magnets.

When the current is passed through the loop, it moves due to the induced force acting on it. After that, a "rider" attached to the loop is pushed outwards from the pivot until the the loop is once against horizontal. By measuring the distance of the rider and the pivot, we can measure the magnitde of the induced force. We repeated the experiment by varying the number of magnets used.

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4. Cathode-ray oscilloscope measurements.

The aim of this experiment was to learn basic skills on how to use a CRO. Such as changing the time base and amplitude divisions etc. The first thing to to do was the verify the accuracy of the source. We connected the source to the CRO through a voltmeter. The results as shown below.


(Image from Yan Yu)
The next step was to connect the source and CRO through a circuit containing a capacitor and resistor. The overlapping sine waves are from different inputs to the CRO from different parts of the circuit.

Continue with Day 2.

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