1. Light and the Photon The Great Max Planck

2. A small problem in 1901 In 1901 most people thought that all of th emajor discoveries in physics had been made. There were a few loose ends to tie up but that is all- so they thought. It was well known that light for instance travelled as waves.Light can do the things that all waves do One of the problems was related to the way in which objects give off light when they are heated

3. Radiating Heat Standard bodies are black Measure the radiation given off by a black body at every frequency of the spectrum at a fixed temperature

4. Changing the temperature Think of a black cooker hot plate. It does not remain black but glows when heated Getting Hotter

6. Wavelength (m) Intensity W/m 2 12000 K 3000 K 6000 K The physics that was known could not quite explain the shape of these curves. It was a small puzzle.

7. After years of struggling with this problem Max Planck was able to give to show that these curves could have the shape they do if they emitted light in “lumps” or “quanta” A single quantum of light would have a tiny amount of energy The word photon was later introduced to describe these lumps. The energy carried by a single photon of electromagnetic radiation is directly related to the frequency of the light Photon Energy = A constant x the frequency of the light This is written as: The constant h is called Planck’s constant. It has a value of 6.63 × 10 -34 Js

8. Questions Radiation typeFrequency(Hz)Energy of a single photon(J) IR Light1.0 x 10 13 Blue light6.7x10 14 X-Ray7.5 x10 18 Γ rays3.0 x 10 20

9. Speed, frequency and wavelength Speed of light = wavelength x frequency rearranging Substituting for f in the Planck formula The speed of light is 3.0 x 10 8 ms -1

10. Questions The table shows the several wavelengths of electromagnetic radiation, calculate the energy of the associated photons in each case Radiation type WavelengthEnergy of a single photon(J) radio3.0m red light700x10 -9 m Blue light400nm Infra red20mm