HOLIDAY ROCK COLLECTION - ROCK GUIDE

Here's an online rock guide you can start using to classify your rocks.

LIGHT + LIGHT = SHADOW

One of the most puzzling physics demonstrations can be one of the most illuminating!
How can a bright flame have a shadow?
It's an example of how electrons can increase their energy state by absorbing photons of light energy and then, when they "fall" back down to their lower energy state, emit a photon of light.
This is a good way to understand quantum theory. The electron can only exist in certain, defined energy states and so the photons absorbed or emitted as they move between any two states will always have the same energy.
Photon energy = Planck's constant (6.63x10^-34 Js) x frequency of light E=hf

And because the frequency of light determines the wavelength (λ=c/f where 'c' is the speed of light), and wavelength determines "colour", these photons will all have the same colour, for any given energy transition.

Which is why, when salt (sodium chloride) is burnt when illuminated by a sodium lamp, the sodium atoms will emit yellow light in the flame, but also absorb the yellow light produced by the sodium atoms in the lamp.

The result is that the flame produces a shadow on a screen.

NEW ZEALAND FROM THE SPACE SHUTTLE

Enjoy this photograph, which the space shuttle commander took for NPBHS student Charley Miles. Space shuttle on the left (tail fin pointing towards Earth) New Zealand on the right!

This makes a superb desktop image.

Click on the photo for the full version.

GEISSLER TUBE

This is a discharge tube. It consists of a partially-evacuated chamber containing an inert gas at low pressure. If a high Voltage (we used an induction coil) is applied across the terminals, the Voltage will strip electrons from the anode and create a stream of electrons. The electrons interact with the gas atoms, producing a visible beam of light.







Now if a magnet is brought close to the tube, the beam of electrons will deflect (moving charge in a magnetic field) and because this deflection is at right-angles to their motion, they move in a circular path.

The closer the magnet, the stronger the magnetic field and the greater the deflection. The force on a moving charge in a magnetic field is F=Bqv .

THE THEREMIN

Invented by the Russian physicist Leon Theremin, the Theremin is the only instrument which is played without touching. The different frequencies and amplitudes of sound are produced by moving your hands near two antennae. This changes the capacitance (and thereby the resonant frequency) of the instrument's LC circuits because your hands act as the grounded plates of capacitors: if your hand moves closer to the the antenna, you are increasing the capacitance; move it further away and the capacitance reduces. Your body is effectively acting as a variable capacitor.
(remember that capacitance is inversely proportional to distance according to C=ε0εrA/d)
The weird and ethereal sound of the Theremin has been used in popular and classical music, and horror and sci-fi films.

NPBHS CREST IN SPACE

The NPBHS tiger-jacket crest presented to NASA by Charley Miles in 2006 is currently in space, aboard the shuttle.
TVNZ Video:

WHAT DO PHYSICS TEACHERS DO IN THEIR HOLIDAYS?

Filmed at the Dunedin Physikos conference 3-6 July 2007.
With thanks to Dr. Des Duthie.

COW'S EYE DISSECTION

Today we dissected cows' eyes.
Although our scalpels and scissors were a bit blunt, we were able to cut up the eyes and see the main features, including the

• lens,
  
• cornea,
  
• aqueous and vitreous humours,
• retina,
• tapetum (the shiny layer that looks like paua shell and reflects light),
• optic nerve.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

Thin Lens Java applet

Have a look at this java applet that simulates spherical lenses and mirrors. Thin Lens Java applet

CHAMPAGNE SPARKLY EFFECT

Total internal reflection can also be seen in a stream of water. By shining laser light through Gladwrap into a stream of water we simulate the fibre optic cable, using water instead of glass. The laser light reflects off the water/air interface and stays inside the stream of water.