EM Waves & Images: Lecture on Electromagnetic Waves & Mirrors, Study notes of Geology

Download EM Waves & Images: Lecture on Electromagnetic Waves & Mirrors and more Study notes Geology in PDF only on Docsity! Lecture 33 Chapter 34 - 35 EM Waves & Images Review • EM waves move at the speed of light, c in free space (vacuum or air) • Speed of light also • Velocity of wave is • Intensity smc /103 8×= λω f k v == m m B Ec = 00 1 εµ =c aveave avg area power area timeenergySI      =     == / EM Waves (27) • Represent light waves as straight lines or rays • If incident (incoming) light wave hits surface of different material some light will – Be reflected back – Travel through and be refracted • If incident beam is ⊥ to surface then no change in its direction EM Waves (28) • Define a line, the normal, which is ⊥ to surface at point where the incident beam hits the surface • Angles relative to normal – Angle of incidence θ1 – Angle of reflection θ1´ – Angle of refraction θ2 • Plane containing incident ray and normal is plane of incidence EM Waves (29) • Law of reflection: Reflected ray lies in plane of incidence and angle for reflection is equal to angle of incidence • Law of refraction: Refracted ray lies in plane of incidence and angle of refraction is related to angle of incidence by Snell’s law 11 θθ =′ 1122 sinsin θθ nn = EM Waves (32) • Traveling from one medium to another – Frequency of wave does not change – Wavelength and velocity do change fv 22 λ= fv 11 λ= 1 2 2 1 2 1 2 1 / / n n nc nc v v === λ λ 2 2 1 1 λλ vv = v cn = EM Waves (33) • n depends on wavelength of light, except in vacuum • Beam consists of different wavelengths, rays are refracted at different angles and spread out – chromatic dispersion • White light consists of components of all the colors in visible spectrum with uniform intensities Fused quartz EM Waves (34) • n for a medium is greater for shorter wavelengths (blue) than for longer (red) • Blue light is bent more than red light EM Waves (36) • The angle of incidence which causes the refracted ray to point directly along the surface is called the critical angle, θc • Angles larger than θc no light is refracted so have total internal reflection EM Waves (37) • Find critical angle from Snell’s law where incident ray is moving from medium with n1 to n2 • For total internal reflection to occur n2 < n1 – Will not happen if moving from air into glass 2211 sinsin θθ nn = 90sinsin 21 nn C =θ 1 21sin n n C −=θ EM Waves (38) • Reflected light is partially polarized • If light incident at Brewster angle its reflected light is fully polarized ⊥ to the plane of incident • Refracted light is still unpolarized Images (1) • Real images – light intersects the image point • Virtual images – light doesn’t really intersect but images appears to come from that point – Sunny day the mirage pool of water on the road is really reflection of low section of the sky in front of you Images (2) • Mirror – surface which reflects light in one direction instead of scattering it in many directions or absorbing it • Plane mirror – flat reflecting surface • Extend reflected rays from O behind mirror • Intersect at point of virtual image I Images (3) • Plane mirror – virtual image I is as far behind the mirror as the object O is in front of it • By convention, object distances p are positive, image distances i for virtual images are negative pi −=