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Unformatted text preview: PHYS 122: Exam II Fall 2001 Prof. N. S. Chant PHYSICS 122
EXAM n — November 14“: 2001
7:00 pm. to 8:00 pm. 1. Please print your name and SIGN your customary signature in ink to identify you and
your examination. Student’s Signature ( in ink please):
Student’s Printed Name:
Recitation Section Number: 0401 2. Also, please initial the following statement whether you wish your score to be posted by
the last four digits of your student ID. number: .t‘ Please DO NOT POST my score. Please POST my score. This test consists of 4 parts, each worth 25 points. The exam is printed on 7 pages and is
to be completed in 1 hour. Please check that you have a complete exam. In most cases partial credit will be given: so show your work. If you need additional space, use the reverse side of the
sheets, or ask for additional paper. Some of the following information may be useful in the exam. k = 9x109 nm2/c2 80 = 8.85x10'12 F/m
speed of sound in air = 345m/s uo = 4 7!: X107 N/A2
charge on electron = 1.6X10‘19C SCORING TABLE (Each student should check the addition of his own score.) PHYS 122: Exam 11 Fall 2001 l. (a) Two parallel wires 2 m apart, 3m long each carry currents of 2A.
(i) (6 points) What is the magnitude of the force between the wires? l; , Me 53332” ' WM
/ : 7 fatal .3... W “ “WW‘WT” Zen; 0) (3 points) If the currents flow in the same direction, isrthe force attractive qr répu‘lsive? Mandi sJﬂ , G) 1 (k) (4 points) What is the total magnetic field at a point exactly“ half way Bgtween the wires? a twin ,3 “a ( flue/t T (D (l) (5 points) Sketch the magnetic field lines due to both wires. Assume the currents both
flow into the page. _ i
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M"*%;m...w~ww (b) (5 points) An electron is moving at a speed of 108 m/s inside
a solenoid along the axis, an‘ow (c). If the magnitude of the
magnetic field inside the solenoid is 2 T, what is the magnitude of the force on the electron? E;Z;T inﬁdli’pslﬂa % Va. ((595 “l5 ' U (9 ayeME! 43} (Sm ﬂ (EX (0) (2 points) If the electron is now moi/mg inside the solenoid at right angles to the axis,
arrow (d), what is the magnitude of the force on the electron? F :1 5; ElmQ PHYS 122: Exam II ' Fall 2001 2. (a) A solenoid of length 0.25m is wound with 4000 turns of wire. The area of the coils is 10"?
m2. The current in the solenoid is 20A. The resultant magnetic field inside the solenoid is given by B = you] where n is the number of turns per unit length. (i) ( 6 points) What is the magnetic field inside the solenoid? Q ; '11:; lg :MO f\ Vii; H \ ax; io‘“‘" we» (Llama 7>C¢ﬁ3€jﬁg m} /X 1T “ 220 at. r7 i” E ., mail}
;;> f; ‘ (ii) ( 6 points )‘ What is the inductance of the solenoid? (iii) (5 points) If the current in the solenoid changes at 20A/sec what back e.m.f is produced? ' '(b) (8 p0ints)‘A utility company produces 120 A of current at 4000 V. The voltage is to be
converted to 240,000 V in order to distribute across country to distant cities. Explain why is it
advantageous to do this. If a transformer is used with a 1000 tum primary coil, how many turns a; needed for the secondary coil? What will the current be in the secondary coil? ,/ 1; 90/5
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u Rt «3 imam \ #333 “if “'1‘ ‘ \\6+ 2‘“; ( 0 AN $.53 PAM G: u {A » PHYS 122: Exam 11 Fall 2001 , 3. (a) (9 points) A beam of light of wavelength 550 nm, traveling in air is incident on a slab of
glass. The incident beam makes and angle of 400 with respect to the normal and the refracted beam makes an angle of 26° with the normal. What is the refractive index for this glass Q what
is the wavelength in the glass? . V” r ‘ Ll ,
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h2 gage mm i (b) (8 points) A diver is 10m below the surface of a pond. The refractive index of water is 1.33.
’ What is his/her apparent depth as viewed from directly above? (c) ( 8 points) The diver now shines a ﬂashlight beam at an angle such that it strikes the surface at
a point 10 m away from a point vertically overhead. Determine whether the ray will appear
above the water or not. Explain. same.» .3; me "We @wHﬁ '7!
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’i’ liq \nl WC ii A 5,642,? m “but: "was PHYS 122: Exam 11 Fall 2001 4. A concave mirror with a focal length of 10 cm is used as a shaving mirror.
a) (7 points) Suppose the user is 11cm from the mirror. Is the image real or Virtual? Is the
image upright or inverted? Is it magnified or diminished? Calculate the final image
position and the (linear) magnification. WWW” iii/Wag, {S Reod, iﬁﬁﬁﬂfmaam maﬁwwuwmwmmm . mumsm. {2 IO M It wt. it p AL) all (1m do A‘ “C m; “at.
f» T “\f .5» db \ rHD b) (7 points) Suppose the user is 7cm from the mirror. Is the image real or Virtual? Is the
image upright or inverted? Is it magnified or diminished? Calculate the final image
position and the (linear) magnification. c) (11 points) Draw a rough ray diagram showing the case where the user is 7cm from the
mirror. Your diagram should be labeled showing the location of the image?"...
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