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 .