Electromagnetic Radiation

1. Electromagnetic Radiation

2. Definitions • Electromagnetic Radiation is energy with wavelike characteristics • Moves at a speed of 3.0 x 108 m/s

3. Wavelength (λ) is the distance between identical points on successive waves – meters • Frequency (ν) is the waves passing per second – unit is the Hertz (Hz)

4. Each type of radiant energy has its own characteristic frequency and wavelength • Short wavelength then high frequency • Long wavelength then low frequency

5. EM Equation • c = νλ • Yellow light given off by a sodium lamp has a wavelength of 589 nm. What is its frequency? • Radiation of high frequency has more energy than that with low frequency

6. Quantum Theory • Rules that govern the gain and loss of energy from an object

7. Max Planck • Said energy comes in “chunks” called quantum • Energy of the quantum depends on the frequency • ΔE = hν • Planck’s constant (h) is 6.63x10-34 J-s

8. Energy Lost or Gained • Total energy lost or gained is a multiple of the quantum • ΔEtot = nhν n – number of quantum

9. Example 1 • Calculate the smallest increment of energy that an object can absorb from yellow light with a wavelength of 589 nm.

10. Example 2 • A laser emits light pulses of frequency of 4.69x1014 Hz and deposits 1.3x10-2 J on energy each pulse. How many quantum of energy is this?

11. Photoelectric Effect • Light shining on certain metals emit electrons • A minimum frequency of light is necessary • Albert Einstein explained this effect with quantum theory

12. Quantum of light is called a photon Ephoton = hν • When photons are absorbed by a metal, energy is transferred to the electrons • If sufficient energy, the electron can overcome the attractive forces holding it in the atom and escape

13. Amount of energy depends on the freq. • If freq is too low, not enough energy for electron to escape • If freq is higher than what is needed for electron to escape, the extra energy is converted into kinetic energy making the electron move faster

14. Total energy of photon = energy required to free electron + kinetic energy • hν = EB + EK

15. Example • Potassium metal must absorb a wavelength of 540 nm (green) or shorter in order to emit an electron. What will be the kinetic energy of an electron if it absorbs 380 nm (UV) light?