Exploring Rutherford's Atom and the Nature of Electromagnetic Radiation

1. Objectives • To review Rutherford’s model of the atom • To explore the nature of electromagnetic radiation • To see how atoms emit light

2. A. Rutherford’s Atom …….but there is a problem here!!

3. When were you last exposed to electromagnetic radiation?

4. B. Energy and Light • What is the nature of electromagnetic radiation? • How are the types of electromagnetic radiation different? • Light can be modeled as a wave, like a wave in water

5. B. Energy and Light • How are the types of light different? c = ν.λ (m) • Wavelength, λ (Greek letter “lambda”) units - m • Frequency, ν (Greek letter “nu”) units - s-1 or Hertz (Hz) • Amplitude, peak height – relates to energy in wave • Speed, c : velocity of light in a vacuum is 3x108 m.s-1 ν (s-1)

6. B. Energy and Light • Electromagnetic radiation

7. Wavelength and Frequency of Visible Light Frequency in Terahertz (1THz = 1012 Hz) and Wavelength in Nanometers (1nm = 10-9 meters)

8. Light Sometimes Behaves in Un-wavelike Ways • The Photoelectric Effect • Light shining on a metal surface can cause electrons to be separated from their atoms • Below a threshold frequency no electrons are emitted however high the intensity • At the threshold frequency electrons start to be emitted • At higher frequencies electrons have additional kinetic energy

9. B. Energy and Light • Dual nature of light – Two co-existing models • Wave • Photon – packet of energy

10. B. Energy and Light • Different photons (from light of different wavelengths) carry different amounts of energy. Energy of photon = h.ν (h is Planck’s Constant )

11. C. Emission of Energy by Atoms • Atoms can give off light • They first must receive energy and become excited. • The energy is released in the form of a photon.