1. G482

4. Standing waves and Progressive waves

5. Standing wave A wave remains in a constant position as a result of interference between two waves travelling in opposite directions. E.g. When the reflected wave interferes with the incident wave in the string.

6. Progressive wave The profile of the wave is moving which indicates a transfer in energy. Energy is moved in the form of vibrating particles.

7. Nodes and Antinodes NODE ANTINODE Node: Point on a standing wave where the wave has no amplitude Antinode: Point on a standing wave where the amplitude/displacement/ particle movement is greatest.

8. Harmonics on strings -1 st -2 nd -3 rd -4 th -5 th -6 th -7 th Harmonics are different modes of vibrations of a wave with increasing frequency and decreasing wavelength.

9. Harmonics in Pipes 1st 3rd2nd 5th3rd 1/2 1 ½ 2 ½ 1 1 2 2 3 3 1 1 2 2 3 3 Wavelength Harmonic

10. If you are given the wavelength and frequency you can work out the speed. 90cm 1 ½ waves WAVELENGTH 90/3 = 30cm 30 x 2 = 60 λ = 0.60m FREQUENCY = 120Hz 120 x 0.6 = 72msˉ¹

11. Polarised light Unpolarised Light A polarisation filter reduces the light in all directions but one. Therefore the light becomes polarised as it is directed in just one way. Light is made up of a large number of transverse waves pointing in all directions. Polarised light Polarisation Filter

12. What happens when you place two Polarisation filters together at exactly 90 degrees? Unpolarised Light A polarisation filter reduces the light in all directions but one. Another polarisation filter reduces the rest of the light to nothing. Light is made up of a large number of transverse waves pointing in all directions. Polarised light Polarisation Filters Therefore no light is let through.

13. Can you think of an example where polarisation is at work? E.g. Sunglasses Glare is light that is reflected off something else. When light is reflected off a surface it becomes polarised. Polaroid sunglasses stop any polarised light perpendicular to the direction of the polarisation filter in the sunglasses. And reduces the intensity from anything less than perpendicular.

14. 45◦ 90◦ MALUS’ LAW 0◦Light is made up of a large number of transverse waves pointing in all directions. If the filter is at 0◦ then 100% intensity is let through. If the filter is at 45◦ then only 50% intensity is let through. A polarisation filter reduces the light in all directions but one.

15. You have to be able to give the differences, similarities and uses of the different waves in the electromagnetic spectrum

16. Similarities All electromagnetic wave: 1.Travel at the speed of light in a vacuum 2.Are transverse waves 3.Are not deflected by electric or magnetic fields 4.Can be polarised 5.Can show interference 6.Can show diffraction

17. Differences BARE IN MIND! – All electromagnetic waves can be described in terms of Photons. They are streams of photons traveling like waves, with each individual photon carrying a certain amount of energy. The only DIFFERENCES between the waves, therefore, is the amount of energy the photons are carrying. With radio-waves carrying the least and Gamma-rays the most.

18. Radio waves What is the wavelength? What is the frequency? Uses: Radio waves are used for the RADIO and radio communication! Difference wave lengths determines the channel

19. Microwaves What is the wavelength? What is the frequency? Uses: Speed cameras Radar Mobile phones Microwave ovens

20. Infrared What is the wavelength? What is the frequency? Uses: Heat lamps Remote controls Video recorders Infrared detector (night vision goggles)

21. Visible light What is the wavelength? What is the frequency? Uses: TO SEE THINGS! Lasers – Laser printers, guns, CD player

22. Ultraviolet What is the wavelength? What is the frequency? Uses: Sterilize products and surgical equipment Black light - Detects forged bank notes Sun tan – Tanning booth

23. UVA Penetrating: Wavelength: UVB Why is it most dangerous?: Wavelength: UVC Penetrating: Wavelength: Most penetrating 320-400 Causes sunburn and skin cancer. Middle penetration. 290-320 Cannot get through Ozone layer 200-290 UVA, UVB and UVC

24. X-rays What is the wavelength? What is the frequency? Uses: Used by doctors to examine internally Used by airport security to check for illegal substances Helps astronomers detect things in space that emit x-rays

25. Gamma Rays What is the wavelength? What is the frequency? Uses: To kill cancer cells in radio therapy Used to sterilize products

26. Superposition The displacement of a medium caused by two or more waves us the algebraic sum of the displacement of the waves.

27. Path difference and Phase difference Phase Difference Difference in distance of two similar points (x axes) from two waves (Red and Blue) and expressed as an angle in radians. Path Difference The difference between the distance travelled for each wave from the origin to a point of interference. E.g. point C. S2 = 6λ and S1 =4λ

28. Coherence What is coherence? If they are coherent then they will have the SAME velocity and be in a constant phase relationship.

29. Young double-slit experiment What do you witness in this experiment? You witness: the interference pattern from two different sources with the same wavelength. Work out the wavelength using the young’s formula How do we accomplish this with light? o To do this with light you must direct a single laser lamp through two slits. o This creates two coherent point sources and the same wavelength of light for both due to the fact you are using a laser. a = fringe spacing D = Distance from screens to slits X = spacing between slits λ = Wavelength What do the symbols stand for?

30. 0.2m 5.0m λ = 30mm Q. Calculate the separation between one region of intensity and the next along the line.

31. What does the λ mean? Wavelength of light (λ) What does the d mean? Distance between grating (d) What does the n mean? Angle between the incident beam and the nth beam (θ) Diffraction Grating

32. dsin θ = n λ Example: Yellow Laser light of wavelength 600nm (6 x 10ˉ⁷m) is transmitted through a diffraction grating of 4 x 10⁵ lines per metre. Q. At what angle to the normal are the first and second order bright lines seen? A. n = 1 (4 x 10⁵) x sinθ = 2 x (6 x 10 ˉ⁷) sinθ = 2 x (6 x 10ˉ⁷)/(4 x 10ˉ⁵) sinθ = θ = A. n = 1 (4 x 10⁵) x sinθ = 1 x (6 x 10 ˉ⁷) sinθ = 1 x (6 x 10ˉ⁷)/(4 x 10ˉ⁵) sinθ = θ = First work out Diffraction grating = 1/(4 x 10⁵) or 4 x 10ˉ⁵

33. Diffraction Grating Q. Why would you use a diffraction grating for light? A. Because you get sharper interference patterns through more slits. Q. If you shine white light through a diffraction grating what do you get? = SPECTRA REMEMBER = Sin values grater than one are impossible. Light can’t be scattered for more than 90˚

34. Intensity Define intensity The rate of flow of energy per unit area. Intensity = P/A!

35. Wave definitions Define: Amplitude Displacement Period Frequency Speed of wave Definitions: Distance from the mean position expressed as a vector 2 times the amplitude Time taken for one complete oscillation Number of waves passing a point per unit time Distance travelled by the wave per unit time Distance from the mean position expressed as a vector 2 times the amplitude Time taken for one complete oscillation Number of waves passing a point per unit time Distance travelled by the wave per unit time