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Version 001 – midterm04review – turner – (92630)1Thisprint-outshouldhave33questions.Multiple-choice questions may continue onthe next column or page – find all choicesbefore answering.Hewitt CP9 28 R1800110.0 pointsWhich travels most slowly in glass?1.Yellow light2.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?µ3.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: 3.9027×10−6J/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.Ifvis the velocity at which the energy istransferred (the velocity of the wave), thenthe relationship between the intensityI(en-ergy per unit time per unit area) and theenergy density of a waveuisI=u cu=Ic=1170 W/m22.99792×108m/s=3.9027×10−6J/m3.Electromagnetic Point Source00310.0 points
Version 001 – midterm04review – turner – (92630)2Light 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.correctExplanation: