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Unformatted text preview: Physics 4 Midterm, Jan. 29, 2009. 12:30 PM
Name: SQ f! l’l:l*0 mg  Seat: Exam form A Do not begin until instructed to do so. We will not answer any questions during the exam because doing so
might unfairly disadvantage those that end up sitting away from the aisles
Where they are unable to ask questions. Because of this, I have carefully
reviewed the wording of the questions to make them clear. This policy may
be a nuisance, but at least it is a fairly applied nuisance. Please do not try to cheat on this exam. It is not likely to help your score,
and it is not worth risking a UC degree for one exam. Some potentially useful reminders:
fcos (@653: = sin (:13)
fsin (15)::52: = — cos (:1?) Ie=mm 1. (8 points) Answer the following true or false questions. 0 (T or® A11 magnetic ﬁeld lines begin at the N pole of a mag et
and end at the S pole. The? chow + insam» 0"" can ~ '(T0I®1}X§::2. gxikzgi
. @orF)£xA'[=0. \zes, Fl 1'5 Parallel 42> {tsL}? c @or F) The lineintegral around any ﬁxed, closed path of the component of the E ﬁeld tangent tg the path is zero if the magnetic
ﬂux is constant in time. S? E ‘32 5 " ‘5 ElaEB/CH: a (T or® The units of EMF are Newtons (N). The. vacF5 ars— U0 H45. 0 ®or F) A magnetic ﬁeld can change the velocity but not the
Speed, of a charged particle moving in it. 5? {s alum»): par pawl Err—ulcer A . +0 V_.
0 (Der F) Two parallel conductors carrying current in the same direction will attract each other. (a —‘“5 (D rFBI. 4+ ’2. FahdS ”P
i z .J. .. i
0 @or F) The unit_s_ for magnetic ﬁeld are N/(A  m). P Paints [151+
F 3 IL?» B 2. (2 points) Suppose that a gold ring is lying in the Xy plane and there
is a uniform and constant magnetic ﬁeld directed along the +zraxis. *
If the ring undergoes thermal expansion, in what direction will the Effaffwﬂ Mtg5
induced current ﬂow?‘lockwise so that )1 points along negative 2". A .&r ”(it (b) counter—clockwise so that {I points along :2. (c) no current will be :g' MOVE “0721;“?
induced in the ring. IVthct cur will afross Hurt.
3. (2 points) Suppose that a conducting ring lies in the Xy plane. If a
current ﬂows in the ring in a direction that is clockwise when Viewed
. . . . . . A
from a pomt on the +2 ans, which directlon does a pomt? d" % 4. (2 points) Considering only the earth’s magnetic ﬁeld, which is about
00001 T, approximately what is the total magnetic flux through the four walls of this room. ﬁat—F0 bthQL SDEAJ A :0 5. (4 points) Consider two vectors: A— — f4 3 0) and B: (0,1,0).
(a). Compute IA} ”H: J4 +3: 3: 5 .4.
(b). Compute B X A. only ﬂ} «ccrmnelmulqr "l1: 8, 50 gm: (0, 103x0’r o 03: FLO 0 "’3 6. (4 points) The ﬁgure below shows four arrangements in which long par
allel Wires carry equal currents directly into or out of the page at the
corners of identical squares Bank the arrangements according to the
magnitude of the net magnetic ﬁeld at the center of the square greatest ﬁrst Dvm B vac—HM" ﬁler 2.0.44. 0? Hug—cur wireS 
I a l '2. , z I 2.
Q “““ @Q ————— @ e  6 e ————— e
i ><a l i #Xi ‘ i 7‘3 ' i R 1
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I 3 “L i I “I E I [pg 1 l {\ i ”(a) 3 *(b) 3 ”(6)3 L’ («:03 7. (10 points) Two circular loops of wire, each of radius R, lie ﬂat on a
table. The centers of the loops are separated from each other by a
distance of BB. As viewed from above, loop 1 is on the right and has
a current in the clockwise direction. L00p 2 is on the left and has a
current in the counter clockwise direction. (a) Draw a representative set of ﬁeld lines produced by loop 1. Include enough information in the drawing to make clear what the ﬁeld looks
like. (b) Draw a representative set of force vectors 0n loop 2, enough to make
clear that you know the force at all points. In what direction is the net
force acting on loop 2. 5i 9 VCLMJ T23?) {GrLL) ' ‘ 61.1“
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CiN‘cLC he! Form. cm a skis cum—6&7! ﬁrm to? 1. 8. (20 points) Prove that the magnetic ﬁeld is uniform everywhere inside
an inﬁnitely long, tightly wound, current—carrying solenoid. You must
Show your work and explain each step to get credit. Sete. /a.¢iv‘ra. Mf—as aortal “Fax—Hoook. 9. (20 points) As shown in the ﬁgure below, a, rectangular loop is near a
long wire. The 100p is a distance R from the wire; it has a width of a
and a height of b. A current I ﬂows through the wire that varies with
time such that [(t) = 3 + ct, with c > 0. Determine the EMF induced
in the loop at t z 1 second. In which direction does the induced current LaaﬁOW? ﬁnerwﬁv 'Wé ﬁatv; R‘vid Hm. EMF: 99M .1; ”=1 Fawraeiafgi 53...“). g: ”CJQE/‘J‘E‘
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