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Exam2Solution - Physics 54 SW Exam 2 Name ”J E 2 Section...

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Unformatted text preview: Physics 54- SW Exam 2 Name ”J E 2 Section: Part E: Short Answer (3pts each) Circle the correct answer: I) @P 10A a—WSA At the point P in between two wires, the magnetic fields from each of the two wires: add and give a net field out of the page. add and give a net field into the page. subtract and give a net field out of the page. subtract and give a net field into the page. 2) A 10 volt battery is connected to a resistor. The resistor overheats, causing the resistance to increase and the current i to decrease rapidly. The currents induced in loops 1 and 2 ., are clockwise in loop 1 and counterclockwise in loop 2. I ‘1 are counterclockwise in loop 1 and clockwise in loop 2. are clockwise in loop I and clockwise in loop 2. are counterclockwise in loop 1 and counterclockwise in loop 2. {a Three volts alternating voltage is applied to the primary winding of a transformer. The primary has 100 turns and the secondary winding has 500 turns. 2 A is flowing the primary. 3) The voltage in the secondary is 0.6 V and the current is 10 A. The voltage in the secondary is 15 V and the current is 0.4 A. The voltage in the secondary is 0.6 V and the current is 0.4 A. d) The voltage in the secondary is 15 V and the current is 10 A. B 4) An electromagnetic wave has an electric field in the positive z~direction and a magnetic field in the positive y—direction. ’% a It is propagating in the x direction. x ) It is propagating in the —x direction. .% K H c) It is propagating in the y direction. N :5 \3 d) It is propagating in the —y direction. y é 3‘. 3 e) It is propagating in the z direction. 0 It is propagating in the ~z direction. @ 2.5W 123 A 20 W linearly polarized laser beam is incident on three polarizers. Polarizer 1 is oriented at an angle 01:450 with respect to the laser field E. Polarizer 2 is oriented at 90° with respect to the laser field E. Polarizer 3 oriented at 45° with respect to the laser field E. The net transmitted power is: [Notez 00345 = 1/sqrt2, c0390 2 O] a) Zero. p g: 20695?%5’ mfg}? mgg?f b) 5W. g 22:92 zzég g d) 10 w. 6) A piece of plastic is thicker at the top than at the bottom and is illuminated with monochromatic light: bottom. The bright fringes in the reflected light are wider at the top than at the bottom. The bright fringes in the reflected light are equally spaced at the top and at the bottom. The reflected light is uniform in intensity. 7) Monochromatic light is incident onto a thin piece of glass, which is suspended in air and of thickness t, giving a minimmn reflection. If the thickness t is doubled: . . . %[email protected] a The reflection IS a max1mum. EThe reflection remains a minimum. “2% m c) The reflection is neither a maximum nor a minimum. "if @ d) The reflection is never a minimum. 8) r 1 Bl B2 B3 An air—spaced capacitor is charging with constant current I flowing into one plate and out of the other. The magnetic field is measured in three places at equal distance from the axis of the wire. a) The magnetic fields measured outside the capacitor at points 1 and 3 are the same, and the field is small at point 2. The magnetic field is the same all three points The magnetic field is varying in time at point 2 and constant at points 1 and 3. d) The magnetic field varies in time at all three points. 9) A current flows through a wire out of the page (black circle) producing a magnetic field with a magnitude B at the location of a charge q (open circle). The charge is moving with velocity v as shown. a) The force on the charge is qu toward the wire. The force on the charge is qu away from the wire. ’2 The force on the charge is zero. d) The force on the charge is qu out of the page. X 10) A current I flows in a wire of length L at an angle 6 to the x—axis.. A magnetic field of magnitude B points into the page. The force on the current ..> has a magnitude [BLsinG and points into the page. ’ has a magnitude [BL and is at an angle 9 to the y~axis. has a magnitude IBLsinG and points at an angle 8 to the y—axis. d) has a magnitude BL and points into the page. Ljart ll: Long Answer 1) (25 pts) Four very long fixed wires (1—4) each carry 10 = 100 A out of the page. A fifth wire (5) carries I = 10 of current into the page. r1 : 0.1 m and r3 = 0.4 m and 6 = 30°. Assume wire 5 is l m long (into the page). Take g = 10 m/s2 and Mo = 471: x 107. a) Find the magnitude of the net magnetic field of wires 1 and of wire 2 at the location of wire 5. Do the same for wires‘igeand 3. b) Show that the net force that wires 1 and 2 exert on wire 5 is along the direction from wire 1 to wire 2 and find its magnitude. Do the same for wires 3 and 4. c) Find the x» and y» components of the net force vector on wire 5, arising from wires l~4. d) How large can the mass of wire 5 be, if it is supported against gravity? w? w @r} 2???) gfizfi‘fiajg 5- %Wfiri’g [email protected]@ ghfi’fier/Qmé a5 a gfigw agar/ew?‘ ggg ear 95 69% 53 e; gay/é a» @o§%[email protected] 7 a gag W m: ea? W §% 4 $2 €> §®W96f§g+§fi is: $2r/ewgfiw 2) (25 pts) A uniform magnetic eld of 2 T points into the page. A current loop is pulled through the field as shown. The width of the loop is w} = 0.50 m at the back and w; := 0.20 m at the front. Assume that v = 10 m/s. a) Find the magnitude of the EM]: induced in the loop. b) If the loop has a resistance of 10 Q, what is the current and which way does it flow (clockwise or counterclockwise). c) What is the net magnetic force on the loop? dag E ff’gff. If; E; fiQ ,da ' W 3: ngVflk/QV}: Q€fl3§jtg an a 6 :2) tale: tag vigkv fifieg/gm QM m @361. ,4; immiggjé M [email protected]@& W Wfi§§€ g ‘2 flag-fig 8,47% £%WN @3223 5‘3} @WWFVWW 3) (20pts) Light travels from a medium of index of refraction r11 = 1.4 to a thin film of index n2 2 1.6, and then out through a medium of index n3 2 1.8. a) What is the thickness t of the central glass slab if a wavelength of 640 nm in air has a maximum reflection in its tenth order. b) For the thickness of part (a), give the 2 longest wavelengths in air that have minimum reflections? ...
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