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Sinusoidal Electromagnetic Radiation

Sinusoidal Electromagnetic Radiation. Acceleration:. Sinusoidal E/M field. Cardboard. Why there is no light going through a cardboard?. Electric fields are not blocked by matter Electrons and nucleus in cardboard reradiate light

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Sinusoidal Electromagnetic Radiation

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  1. Sinusoidal Electromagnetic Radiation Acceleration: Sinusoidal E/M field

  2. Cardboard Why there is no light going through a cardboard? Electric fields are not blocked by matter Electrons and nucleus in cardboard reradiate light Behind the cardboard reradiated E/M field cancels original field

  3. Effect of E/M Radiation on Matter • Radiative pressure – too small to be observed in most cases • E/M fields can affect charged particles: nucleus and electrons Both fields (E and M) are always present – they ‘feed’ each other But usually only electric field is considered (B=E/c)

  4. Effect of Radiation on a Neutral Atom Main effect: brief electric kick sideways Neutral atom: polarizes Electron is much lighter than nucleus: can model atom as outer electron connected to the rest of the atom by a spring: F=eE Resonance

  5. Radiation and Neutral Atom: Resonance Amplitude of oscillation will depend on how close we are to the natural free-oscillation frequency of the ball-spring system Resonance

  6. Importance of Resonance E/M radiation waves with frequency ~106 Hz has big effect on mobile electrons in the metal of radio antenna: can tune radio to a single frequency E/M radiation with frequency ~ 1015 Hz has big effect on organic molecules: retina in your eye responds to visible light but not radio waves Very high frequency (X-rays) has little effect on atoms and can pass through matter (your body): X-ray imaging

  7. Refraction: Bending of Light In transparent media, the superposition can result in change of wavelength and speed of wavefront • Index of refraction of medium, • Depends upon wavelength • and properties of medium Rays perpendicular to wavefront bend at surface

  8. Refraction: Snell’s Law A ray bends as it goes from one transparent media to another

  9. Example of Snell’s Law A ray travels from air to water

  10. Total Internal Reflection Reflection and transmission For small W? =.75 =.96 =1.15

  11. Prisms and Lens Convergent lens Divergent lens

  12. Prisms and Lens Lens is flat in center and prism angle steadily increases as y increases

  13. Thin Lenses How does the deflection angle depend on the height, ? 2y y For converging lenses parallel rays cross the axis at the focal distance from the lens When changes by factor of 2 change prism angle changes by factor of 2

  14. Deviation doesn’t depend on incident angle Add to the 2nd perpendicular For small angles, using Snell’s law and ; is the incident angle (air to glass) ; is the refracted angle (air to glass) ; is the incident angle (glass to air) So the deviation angle is independent of the ; is the refracted angle (glass to air)

  15. y Thin lens formula

  16. Images • Images are formed where rays intersect • Real image: rays of light actually intersect • Virtual image: rays of light appear to intersect

  17. Lenses • A lens consists of a piece of glass or plastic, ground so that each of its two refracting surfaces is a segment of either a sphere or a plane • Converging lenses • Thickest in the middle • Diverging lenses • Thickest at the edges

  18. Focal Length of a Converging Lens • The parallel rays pass through the lens and converge at the focal point • Focal length is positive.

  19. Focal Length of a Diverging Lens • The parallel rays diverge after passing through the diverging lens • The focal point is where the rays appear to have originated (focal length is negative)

  20. Converging Lens, image object • The image is real and inverted

  21. Converging Lens, image object • The image is virtual and upright • Magnifying glass Magnification

  22. Diverging Lens object • The image is virtual and upright

  23. Photolithography A photomask is imaged onto the surface of a semiconductor substrate in the production of an integrated circuit. The mask is 0.25 m in front of a lens (0.25m), and the focal length of the lens is 0.05m. What should be the distance of the semiconductor surface behind the lens, ?

  24. Plane or Flat Mirror object image Magnification

  25. Spherical Mirrors • A spherical mirror has the shape of a segment of a sphere • A concave spherical mirror has the silvered surface of the mirror on the inner, or concave, side of the curve • A convex spherical mirror has the silvered surface of the mirror on the outer, or convex, side of the curve

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