Light, Waves and Particles

1. Light, Waves and Particles Physics 113 Goderya Chapter(s): 6 Learning Outcomes:

2. Light as a Wave (1) l c = 300,000 km/s = 3*108 m/s • Light waves are characterized by a wavelength l and a frequency f. • f and l are related through f = c/l

3. Light as a Wave (2) • Wavelengths of light are measured in units of nanometers (nm) or Ångström (Å): 1 nm = 10-9 m 1 Å = 10-10 m = 0.1 nm Visible light has wavelengths between 4000 Å and 7000 Å (= 400 – 700 nm).

4. Light as Particles • Light can also appear as particles, called photons (explains, e.g., photoelectric effect). • A photon has a specific energy E, proportional to the frequency f: E = h*f h = 6.626x10-34 J*sis the Planck constant. The energy of a photon does notdepend on the intensity of the light!!!

5. Light and Other Forms of Radiation • The Electromagnetic Spectrum In astronomy, we cannot perform experiments with our objects (stars, galaxies, …). The only way to investigate them, is by analyzing the light (and other radiation) which we observe from them.

6. Wavelengths and Colors Differentcolors of visible light correspond to different wavelengths.

7. F3-1 • Electromagnetic (EMW) wave

8. F3-2 • Model • Electric and Magnetic fields.

9. F3-3 The EMW properties- Speed • Electromagnetic waves are transverse waves. • Wavelength x frequency = speed of light

10. F3-4 The EMW properties-Energy E = h x f E = h c/l h = Planck’s Constant 6.6 x 10 -34 J.s c = 3 x 108 m/s

11. Light and Other Forms of Radiation • The Electromagnetic Spectrum In astronomy, we cannot perform experiments with our objects (stars, galaxies, …). The only way to investigate them, is by analyzing the light (and other radiation) which we observe from them.

12. F3-7 Wavelength 400 nm • The visible light • ROYGBIV 500 nm 550 nm 600 nm 700 nm Frequency

13. The Electromagnetic Spectrum Wavelength Frequency High flying air planes or satellites Need satellites to observe