midterm_04_review - Version 001 midterm 04 review turner(92630 This print-out should have 33 questions Multiple-choice questions may continue on the

# midterm_04_review - Version 001 midterm 04 review...

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Version 001 – midterm 04 review – turner – (92630) 1 This print-out should have 33 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. Hewitt CP9 28 R18 001 10.0 points Which travels most slowly in glass? 1. Yellow light 2.Violet lightcorrectAt what distance from a 50 W electromag-netic wave point source (like a light bulb) isthe amplitude of the electric field 39 V/m?µ 3.Green light4.Orange light5.Brown light6.Blue light7.Red lightExplanation:n=cvSince violet light is refracted more thanthe light of other frequencies its index of re-fraction is the highest, making its speed thesmallest.In other words, violet light travelsslowest in glass.Energy of Sunlight00210.0 pointsThe intensity of sunlight under the clear skyis 1170 W/m2.How much electromagnetic energy is con-tained per cubic meter near the Earth’s sur-face? The speed of light is 2.99792×108m/s.Correct answer: 3.9027×106J/m3.Explanation:Let :I= 1170 W/m2andc= 2.99792×108m/s.oc= 376.991 Ω.Correct answer: 1.40442 m.Explanation:Let :P= 50 W,Emax= 39 V/m,andµ0c= 376.991 Ω.The wave intensity (power per unit area) isgiven byI=Sav=E2max2 (µoc)=(39 V/m)22 (376.991 Ω)= 2.01729 W/m2.The constantµoc(impedance of free space)turns out to be 120πΩ.You should verify that (V/m)2Ω = W/m2.With this we can find the intensity, whichmultiplied by the area of a circle of radiusRmust gives us the source’s powerP, therefore4π R2I=P= 50 W.Solving for the radius we get,R=radicalbiggP4π I=radicalBigg50 W4π(2.01729 W/m2)=1.40442 m. If v is the velocity at which the energy is transferred (the velocity of the wave), then the relationship between the intensity I (en- ergy per unit time per unit area) and the energy density of a wave u is I = u c u = I c = 1170 W / m 2 2 . 99792 × 10 8 m / s = 3 . 9027 × 10 6 J / m 3 . Electromagnetic Point Source 003 10.0 points
Version 001 – midterm 04 review – turner – (92630) 2 Light Wave in Water00410.0 pointsA light wave passes from air into water.Which of the following is true? 5.Its frequency remains unchanged, but itswavelength decreases.correct Explanation: