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Exam 2a Solutions - 1 A conducting loop of wire is placed...

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Unformatted text preview: 1. A conducting loop of wire is placed in a magnetic field that is normal to the plane of the loop. Which one of the following actions will not result in an induced current in the loop? CA) Rotate the loop about an axis that is parallel to the field and passes through the center Eff ”’ of the loop. B) Increase the strength of the magnetic field. C) Decrease the area of the loop. D) Decrease the strength of the magnetic field. E) Rotate the loop about an axis that is perpendicular to the field and passes through the center of the loop. ; a»..- J Msfifij it §é% “75. I i. A conducting bar moves to the left at a constant speed V: 1 m/s on two conducting rails in a constant magnetic field B=0.5 T. The rails are joined at the left as shown. Originally the dimensions of the loop are height h= 0.5 m and length l=1 m. Determine the induced emf in the loop. 3. A conducting loop has an area of 0.065 m2 and is positioned such that a uniform magnetic field is perpendicular to the plane of the loop. When the magnitude of the magnetic field decreases to 0.30 T in 0.087 s, the average induced emf in the loop is 1.2 V. What is the initial value of the magnetic field? A) 0.42 T B) 0.75 T C) 0.87 T 12) 1.2 T $133} 1.9 T 4. A long, straight wire is in the same plane as a rectangular, conducting loop. The wire carries a constant current] as shown in the figure. Which one of the following statements is true if the wire is suddenly moved toward the loop? a; if _ _ 2* QM, A) There will be no induced emf and no induced current. B) There will be an induced emf, but no induced current. ‘wf C There will be an induced current that is clockwise around the loop. . ____ WThere will be an induced current that is counterclockwise around the loop. Agvfiéffw fiflwfi‘g‘wef E) There will be an induced electric field that is clockwise around the loop. g f IA 1”“ {M at; {frag}: up} w mafia erw’iafiwmxf Use the following to answer question 5. A single conducting loop with an area of 2.0 m2 rotates in a uniform magnetic field so that the induced emf has a sinusoidal time dependence as shown. M 15 ’1'” 3.175 1251‘ 1,535. . XJ.11.5 / -151; V kg” \J 5. With what angular frequency does the loop rotate? A) 0.16 rad/s B) 0.30 rad/s C) 052 rad/s x9“) 0.80 rad/s g 3:31.26 rad/s MM Page 2 6. The current in the secondary coil of a step—up transformer is 16 A when the current in the primary coil is 48 A. Determine the turns ratio, Ns/Np, of the transformer. A 3 , ‘ C) 033 N1 D) 0.24 A; c... E) 0.48 N1: } ”can MM , J 1": TE) ”a? _ 7 Which one of the following statements concerning electromagnetic waves is false? I A) Electromagnetic waves carry energy. V" 1. f. .. , @X— —rays have longer wavelengths than radio waves. K E am; gtfflr‘w E I i C) In vacuum, all electromagnetic waves travel at the same speed. V D) Lower frequency electromagnetic waves can be produced by oscillating circuits. V” E) They consist of mutually perpendicular electric and magnetic fields that oscillate W . perpendicular to the direction of propagation. 8. The average distance between the surface of the earth and the surface of the sun is 1.5 * 1011 111. How much time, in minutes, does it take light leaving the surface of the sun to reach the earth? A) zero minutes n\ qn*1n 3m:“ 13);.) 1U 1111.11 CD 8 3 min W M» 1 n. a} éfi} aafi w D) 74 min B) 500 min a twat 9. An electromagnetic wave has an electric field with peak value 250 N/C. What is the average intensity of the wave? A) 0.66 W/mz $1 .1“. g B) 0.89 W/mz ti “”5 i , 1 f” 2 t. W M?” D) 120 W/m2 34 E) 170 W/m2 Page 3 10. An astronomer observes electromagnetic waves emitted by oxygen atoms in a distant galaxy that have a frequency of 5.710 * 1014 Hz. In the laboratory on earth, oxygen atoms emit waves that have a frequency of 5.841 * 1014 Hz. Determine the relative velocity of the galaxy with respect to the astronomer on the earth. Note: The speed of light is 2.9979 * 108 m/s. (e W M 9 _ W 74 ‘ .724 *106 m/s, away from earth film ”93%“ a: {3 ’ fig; i d} g E“ m 6724* 106 m/s, toward earth g mam? ’“ “a lm fi 5? fife C) 2.931 * 108 m/s, away from earth D) 4369* 104 m/s, toward earth t; t“ ( g :_ gar? E) 4.369 * 104 m/s, away from earth xi,“ 4 C” / tilt r U“ i l i (‘1, 97%»? fail Wyatt mam/4w /: 11. The focal length of a spherical concave mirror is 20 cm. What is its radius of curvature? A) 5 cm B) 10cm Umim “it: é. gm :WZj C) 20 cm E) 50 cm MM Page 4 Use the following to answer question 12. An object is placed in front of a concave spherical mirror as shown below. The three rays 1, 2, and 3, leave the top of the object and, after reflection, converge at a point on the top of the image. Ray 1 is parallel to the principal axis, ray 2 passes through F, and ray 3 passes through C. B) 2 only C) 3 only D) both 1 and 2 E) 1, 2, and 3 13. A convex mirror in an amusement park has a radius of curvature of 3.00 m. A man stands in front of the mirror so that his image is half as tall as his actual height. At what distance must the man focus his eyes in order to see his immée? 3.00m L if ,0 My ” "“ C) 4.50m D) 5.00m , i E) 6.75m w i M WW3.» ff: 5:? 5;“ W gti 5:3 f: r CACXW WWWQWIQWI “ ~~~~~~~~ “ {Saw/s M “no. a 5:? ii: i f“) g . .2, 2:} f U? E? f: / Maw M {1'17 ,2: a, W , W 0 Manama,” M»? 3W” x“? w i Page 5 MWMWWW WM, . , p g "’e m M A q ; I “”5; a Wm gram 5% raw 14. The table lists the index of refraction for various substances at 20 0C for light with a wavelength of 589 nm in a vacuum. Through which substance will light with a vacuum wavelength of 589 nm travel with the greatest speed? Substance n g g wt \ .1 k .3 fused quartz 1.458 ’ WWW fl 3; ..... 5: if wig :K‘m - 5:: PM f, ethyl alcohol 1.362 EWMi )2. m 5% W crown glass 1.520 1 E A [if carbon tetrachloride 1.461 E Q 38$ W 3% 13a... W. M- My: . ,, crystalline quartz 1.544 1 A) fused quartz fig) crown glass 5‘" 5) ethyl alcohol % carbon tetrachloride E) crystalline quartz 15. The bending of light as it moves from one medium to another with differing indices of refraction is due to a change in what property of the light? A) amplitude fl . B) period , ., Wjfi a H frequency /ng} {fig} 3 speed ) color 16. A ray of light propagates in water (n = 1.33) and strikes a sheet of glass (11 = 1.67). If the angle of refraction in the glass is 30°, determine the angle of incidence. A) 303° B) 32.80 C) 35.20 Page 6 Use the following to answer question 19. A 4.0—cm object is placed 30.0 cm from a converging lens that has a focal length of 10.0 cm as shown in the diagram. Note: The diagram is not drawn to scale. Dbjectfi .rr muwmamw 4: MMfiJéV—wT/x‘éwrmx‘fiwWrflwkwrrwowfivz»wb‘fl m» m ‘ row—~— 31.111 cm W: 19. Determine the height and orientation of the image. A) 2 cm and upright 1 cm and inverted 8 cm and upright W _ E) 8 cm and inverted W , 20. Which one of the following statements best explains why chromatic aberration occurs in lenses, but not in mirrors? A) The shape of the mirror prevents chromatic aberration. B) The thickness of a lens varies from top to bottom. C) The frequency of light changes when it passes through glass 4%”) The angle of incidence varies over the surface of a lens for incident parallel rays of light. {Kiwifferent colors of light are refracted by different amounts as the light passes through a lens. 1 W A am! as W“ ’tW” Page 8 17. A glass block with an indeX of refraction of 1.7 is immersed in an unknown liquid. A ray of light inside the block undergoes total internal reflection as shown in the figure. Which one of the following relations best indicates what may be concluded concerning the index of refraction of the liquid, nL? if) if: 1 i? S 3 r‘ t“ IV /\ s [V fi—‘p—ah—‘Hh—fi prnI—ib ~ 9 ll\[/\ @ga w :> 1 \./\../\./ S 3 t" F" t" 18. Which one of the following statements is true concerning the focal length of a lens? A) The focal length is the same for all colors B) Ihe focal length is different for different colors because of reflection ,. 1. ,, e focal length is different for different colors because of dispersion D) The focal length is different for different colors because of polarization. E) The focal length is different for different colors because of spherical aberration. Page 7 ...
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