Lecture_27_Part_1 - 4 1" = = = c E c E E c c S Note What if we have a reflective surface 2 N/m 6 10 3 9" = Total force on the sail N 3 9 =

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E field starts motion • Moving charge in magnetic field: B v q F mag ! ! ! ! = F mag What if there is negative charge? B v q F mag ! ! ! ! " = F mag ‘Radiation pressure’: What is its magnitude? Average speed: v/ 2 c E v q B v q F mag 2 2 = = 1 2 ) /( 2 << = = c v qE c E v q F F elec mag Momentum of E/M Radiation
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Net momentum: in transverse direction: 0 in longitudinal direction: >0 Relativistic energy: E 2 = pc ( ) 2 + mc 2 ( ) 2 Quantum view: light consists of photons with zero mass: ( ) 2 2 pc E = Classical (Maxwell): it is also valid, i.e. momentum = energy/speed B E S ! ! ! ! = 0 1 μ ) N/m (in 2 B E c c S ! ! ! ! = 0 1 Momentum flux: Momentum Flux
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What is the force due to sun light on a sail with the area 1 km 2 near the Earth orbit (1400 W/m 2 )? Solution : N/C 725 0 = = ! c flux E B E c c S ! ! ! ! = 0 1 μ 2 N/m 6 2 0 2 0 10 65
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Unformatted text preview: . 4 1 ! " = = = c E c E E c c S ! Note: What if we have a reflective surface? 2 N/m 6 10 3 . 9 ! " = Total force on the sail: N 3 . 9 = F Exercise: Solar Sail Atmospheric pressure is ~ 10 5 N/m 2 Electric fields are not blocked by matter: how can E decrease? Re-radiation: Scattering Positive charge 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...
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This note was uploaded on 04/02/2008 for the course PHYS 272 taught by Professor K during the Winter '07 term at Purdue University-West Lafayette.

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Lecture_27_Part_1 - 4 1" = = = c E c E E c c S Note What if we have a reflective surface 2 N/m 6 10 3 9" = Total force on the sail N 3 9 =

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