Light & the Electromagnetic Spectrum

1. Light & the Electromagnetic Spectrum

2. What do you see? Old woman? Or young girl?

3. Question • Is turning a light on and off a chemical or physical change? • Physical change • What creates light?

4. UV Light • Bohr Model – electrons are found in nrg levels Visible Light Infrared Light

5. Niels Bohr

6. Niels Bohr • 1913, looked at a hydrogen atom • Suggested an e- could move between nrg levels if discrete photons or nrg (amounts of nrg) were absorbed or emitted by the e- • e- falls from high  low nrg = photon emission • Photon has a frequency, or color, that matches the e- fall

7. Light • When an electron moves from an excited state to its ground state, light nrg is given off. • Excited atom~ e- not in lowest possible nrg state • They have absorbed nrg and jumped to a further nrg level • The color of the light depends on the amount of nrg. • The more nrg levels jumped, the greater the nrg of light.

8. Light • e- at higher nrg states are not stable • These e- want to return to their ground state to become stable • Lowest possible nrg level • Distance between nrg levels is NOT all the same.

9. Electromagnetic Spectrum ROYGB I V • Blue light has a higher frequency than red.

10. Frequency – the # of wave cycles passing a point in a period of time. • As frequency increases, wavelength decreases.

11. Max Planck • Planck assumed energy can be released and absorbed in discrete packets called quanta. • The energy of one quanta is: Where, known as Planck’s constant.

12. Light of a particular wavelength (λ) has a particular frequency (ν) and nrg (E). • If ν, λ or E are known, the other 2 can be calculated. speed of light Planck’s constant

13. Practice • Yellow light given off by a sodium vapor lamp has a wavelength of 589 nm. What is the frequency of this radiation?

14. Beware of UNITS! • Unit for frequency (ν) • Hertz • Unit for wavelength (λ) • Meter (m) or nanometer (nm) • Unit for energy (E) • Joule ( J )

15. Practice • Calculate the energy of one photon of yellow light whose wavelength is 589nm.

16. Pop Quiz! • What do the following symbols stand for? What are their units? • ν • λ • h • c • E Frequency Wavelength Planck’s Constant Speed of Light Energy

17. Light’s wave nature is seen as its ability to diffract, reflect, refract.

18. Wave Particle Duality of Light • Planck stated that nrg is radiated in discrete packets called quanta. • A photon is a quantum of light having the energy • Light’s particle nature is seen by the emission spectra of elements.

20. Why each element produces a unique line spectra.

22. Eventually leads to a very famous equation by a very famous scientist.