1 / 18

Modern Physics

Modern Physics. The Saga of Quantization. The Saga Begins…. Blackbody Radiation – radiation (electromagnetic waves) emitted by an object due to vibrating electrons. Emitted over a band of frequencies…but some frequencies are more intense than others. It Depended on Temperature.

franklindunn
Download Presentation

Modern Physics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Modern Physics The Saga of Quantization

  2. The Saga Begins… • Blackbody Radiation – radiation (electromagnetic waves) emitted by an object due to vibrating electrons. • Emitted over a band of frequencies…but some frequencies are more intense than others.

  3. It Depended on Temperature • The peak of the curve is in a different wavelength regions for different temperatures. • The peak could be predicted: lp T = 2.90 x 10-3 m K

  4. Exploring Wein’s Law • Look at the type of EM waves emitted UO Applet • What things do you notice? • P 782 # 6 lp T = 2.90 x 10-3 m K (18 x 10-9) T = 2.90 x 10-3 m K T = 1.61 x 105 K lp (2000 K) = 2.90 x 10-3 m K lp = 1.45 x 10-6 m = 1.45 mm

  5. The Shape of the Curve • But while the peak could be predicted, the rest of the curve could not be predicted using classical theory.

  6. Planck’s Hypothesis • Max Planck then said, well what if not EVERY value is allowed. • He realized that only integer multiples were allowed and the step size was constant: E = h f h = 6.626 x 10-34 J s (Planck’s Constant)

  7. What does it mean? • It means that energy actually comes in packets. • We cannot have any speed we want, only those that correspond to the energy steps. • We cannot have any frequency we want, only those that correspond to the energy steps. • Quantum mechanics was born.

  8. Why hadn’t we noticed it yet? • Big things are quantized, but if the step is small, then we do not notice the steps. • But when we get to small things, we start to notice the steps. • What things are small enough?

  9. Calculating Energy • All energy can be calculated for all wave properties as: E = h f (quantized energy) Example: Light at 5.15 x 1014 Hz E = 6.62 x 10-34 (5.15 x 1014) = 3.4 x 10-19 Joules

  10. Photons • But Joules per what? • Joules per photon! That means that light is both a wave and a particle. (We have heard this before…we see how we know this later on!) • If light is both a wave and a particle, then why can’t everything be a wave and a particle!

  11. Wave Particle Duality • Everything IS both a wave and a particle! • de Broglie then calculated the wavelength of any object: l = h / (mv) l = h / p (where p is momentum!)

  12. Your Car’s Wavelength • Let’s calculate your car’s wavelength on the freeway: l = 6.62 x 10-34 / (1000 kg * 25 m/s) = 2.6 x 10-38 m

  13. Let’s Try Something Smaller • Electrons have less mass and move faster… • = 6.62 x 10-34 / (9.11 x 10-31 * 1 x 105 m/s = 7.2 x 10-9 m = 7.2 nm Now that is something we can measure!

  14. The Diffraction of Electrons • Electrons have mass and are particles, but diffraction is a wave property!

  15. What about particles that don’t have mass? • l = h / (mv) • l = h / p (where p is momentum!) • Now we can calculate the momentum of a mass-less particle: • p = h / l

  16. Photon Momentum • What is the momentum of a photon of red light, wavelength = 650 nm? • We cannot calculate p = mv; we have the speed of light, but photons are mass-less! • l = h / p • 650 x 10-9 m = 6.62 x 10-34 / p • p = 1.01 x 10-27 kg m/s • This is why photons can be used to power space ships.

  17. Whiteboards • P 782 # 5, 37, 40, 44, 45

More Related