1. Dual Nature of Light
Then there was light!

2. TIMELINE Nature of light- wave or particle?
1600’s Isaac Newton says light consist of tiny particles
1864 Maxwell says light acts like a wave similar to water.
19th century found that each element products a characteristic spectrum of light.

3. Max Planck used idea of quanta (discrete units of energy to explain hot glowing matter. (1900) (E = hf)
Albert Einstein used light as photons to explain the photoelectric effect. (1903)
When a photon hits the surface of the metal, it transfers its energy to the electron. Energy of photon vs number of photons.
Louis de Broglie discovered that electrons had a dual nature-similar to both particles and waves.(1923)

4. Heisenberg described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of uncertainty-cannot know both the position and velocity of a particle. (1927)
Schrödinger viewed electrons as continuous clouds and introduced “wave mechanics” as a mathematical model of the atom. (1930)

5. Light as a Wave
Longitudinal: particle displacement is parallel to the direction of wave propagation.
Transverse: particle displacement is perpendicular to the direction of wave propagation.
Traveling:wave that moves in time.
Standing:occurs in such a manner that there are specific points that appear to be standing still.

6. Light... Reflects: bounces off an object
refracts: pass through one medium to another.
Diffracts:changes direction as they pass through an opening or around an obstacle.
shows interference

7. Electomagnetic Spectrum

8. Continuous spectrum: white light passes through a prism. (rainbow)
Bright line spectrum: when elements are heated.
Each element has its own spectra or set of fingerprints.

9. Properties of Waves
Wavelength: the distance between successive crest of the wave. Measured in meters. (visible = 400 nm to 750 nm)
Frequency: number of peaks that pass a point each second. (Hz= cycle/s)
Amplitude: distance from rest to crest.
Velocity: distance a peak moves in a unit of time.
Speed of light: 3.00 x 108 m/s in a vacuum C=fλ

10. Light as a Particle 1600 Isaac Newton says light is a particle
Max Planck says excited atoms radiate energy in discrete packets called quanta.
Albert Einstein describes the photoelectric effect. When a photon (packet of energy) hits the surface of the metal, it transfers its energy to the electron. There is a discharge of electrons from matter by impact of radiation .

11. Compton effect: a photon can collide with an electron after the collision, the photon travels at the speed of light.