Acceleration: Sinusoidal E/M field Sinusoidal Electromagnetic Radiation

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 Cardboard

1.Radiative pressure – too small to be observed in most cases 2.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) Effect of E/M Radiation on Matter

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

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

E/M radiation waves with frequency ~10 6 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 ~ 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 Importance of Resonance

In transparent media, the superposition can result in change of wavelength and speed of wavefront Refraction: Bending of Light Rays perpendicular to wavefront bend at surface

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

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

Reflection and transmission Total Internal Reflection

Prisms and Lens Convergent lensDivergent lens

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

Thin Lenses 2y2y For converging lenses parallel rays cross the axis at the focal distance from the lens y

For small angles, using Snell’s law Deviation doesn’t depend on incident angle

y Thin lens formula

Images Images are formed where rays intersect –Real image: rays of light actually intersect –Virtual image: rays of light appear to intersect

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

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

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)

The image is real and inverted object image

The image is virtual and upright object image Magnifying glass

Diverging Lens The image is virtual and upright object

Photolithography Choice A0.05 B C0.01 D0.125 E0.25

Plane or Flat Mirror objectimage

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