Quiz on Thursday

1. Introduction to Physical ScienceMonday, Wednesday, ThursdayTom Burbinetomburbine@astro.umass.edu

2. Quiz on Thursday • Magnetism • Waves • Light • c = λ*f • E = h*f • Electromagnetic spctrum • Doppler shift

3. Wave • Something that vibrates in space and time • Light acts as a wave • Sound acts as a wave

5. Frequency • The number of vibrations per unit time

6. Light • Light is a form of energy

7. Light • These are all forms of light • Gamma rays • X-rays • Ultraviolet light • Visible light • Infrared light • Radio waves

8. Light • Can act as a particle • Can also act as a wave

9. Particle aspect • Particles called photons stream from the Sun and can be blocked by your body

10. Photons • Light is quantized • Comes in discrete packets called photons

11. Wave aspect

12. Thomas Young Experiment • http://micro.magnet.fsu.edu/primer/java/interference/doubleslit/

13. Characteristics of waves • velocity = wavelength x frequency • Wavelength = distance • Frequency = cycles per second = hertz 3 x 108 m/s

14. Speed of sound • Speed of sound = 340 m / s

15. For light • c = wavelength x frequency • In vacuum, speed of light stays the same • So if wavelength goes up • Frequency does down • f = frequency • λ = wavelength • c = λ x f

16. Calculations • c = λ x f • So if the wavelength is 1 x 10-12 m • 3 x 108 m/s = 1 x 10-12 m * f • f = 3 x 108 m/s/1 x 10-12 m • f = 3 x 1020 s-1 = 3 x 1020 Hz

17. Calculations • c = λ x f • So if the frequency is 1 x 1015 Hz • 3 x 108 m/s = λ * 1 x 1015 Hz • λ = 3 x 108 m/s/1 x 1015 Hz • λ = 3 x 10-7 m

18. Energy of light • Energy is directly proportional to the frequency • E = h * f • h = Planck’s constant = 6.626 x 10-34 J/s • since f = c/λ • Energy is inversely proportional to the wavelength • E = hc/λ

19. Higher the frequency, Higher the energy of the photon Higher the wavelength, Lower the energy of the photon

20. Calculations • What is the energy of a radio wave with a frequency of 1 x 107 Hz? • E = h * f • h = Planck’s constant = 6.626 x 10-34 J/s • E = 6.626 x 10-34 J/s * 1 x 107 • E = 6.626 x 10-27 J

21. Calculations • What is the energy of a gamma ray photon with wavelength of 1 x 10-15 m • E = hc/λ • h = Planck’s constant = 6.626 x 10-34 J/s • E = 6.626 x 10-34 J/s * 3 x 108 m/s / 1 x 10-15 m • E = 1.99 x 10-10 J

22. So why are some types of radiation dangerous? • Higher the energy, the farther the photons can penetrate • So gamma and X-rays can pass much more easily into your the body • These high-energy photons can ionize atoms in cells • Ionization means removes electrons from an atom

23. More dangerous

24. http://www.arpansa.gov.au/images/basics/emr.jpg

25. ROYGBIV • ROYGBIV • Red – long wavelength • Violet – short wavelength

26. Doppler Shift • If a light or sound source moves towards you, the wavelength you measure (hear) from the source decreases • Frequency increases • If a light or sound source moves away from you, the wavelength you measure (hear) from the source increases • Frequency decreases

27. http://www.youtube.com/watch?v=-t63xYSgmKE&feature=related

28. Doppler Shift http://www.psi.edu/~esquerdo/asp/shifts.jpg

30. http://www.youtube.com/watch?v=a3RfULw7aAY

31. Wavelength http://www.psi.edu/~esquerdo/asp/method.html

32. Any Questions?