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Unformatted text preview: PHYS 212 First Hour Exam Name February 12, 2008 Problem Sessi n Instr:
Hour: Show all work for full credit! Answers must have correct units and appropriate number of significant digits. For all the problems (except for multiple choice questions), start with some combination of (a) a fundamental equation (b) a sentence explaining your approach;
or (c) a sketch. k=8.99><109Nmz/C2 e=1.60x10‘19c me=9.11x10‘3‘kg mp=1.67x10'27kg p0 = 4nx10‘7 N/A2 80 = 8.85X10‘12 C2/1\I'm2 g = 9.8 m/s2 1. (15 pts) An electron with speed 1.4 x 104 m/s moves in a region with uniform magnetic ﬁeld B = 2.1 T directed out of G
the page as indicated in the ﬁgure. Calculate the magnitude of the magnetic force experienced Q \
by this particle, and clearly indicate the direction of the
force vector on the f1 gure. E
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bi: if :15 Offwii'e dxﬁj Slim. b ;> 1: 3“ ﬂ K negofivlé 2. (15 pts) Two large parallel plates are separated by a QV @
distance 6.0 cm. The left plate has electric potential of +200 V. A particle with mass 12 g and charge —0.26 C
starts at rest at the left plate and is accelerated toward the other plate. It reaches the right plate with a speed of 78 m/s. Determine the electric potential of the second
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f/afz 2. mad/— 4N hcgémpo/mﬁa/ VJ M+AV= Zara NW 1 5% U. 3. (8 pts) The total electric ﬂux through some spherical surface is zero. Is the electric
ﬁeld at the surface of the Sphere necessarily zero? Explain why or why not. M2. ”5;;‘5 173 m Magda/V7 m/ E mpg/W WM
MW éM Mu; 7’7);er {mm 40/an (MM/6M4  4. (18 pts) Consider a uniform line of charge of length L that lies along the x—axis a
distance 5 from the origin. The total charge on this line is Q. We want to determine
the electric field at the point P located on the y—axis a distance h above the origin. Set up the integral expression for (lg y
Ey, the y—component of the (
electric field. Your answer must 6
be in terms of fundamental
constants, the quantities given
above, and an integration variable. Do not evaluate the
integral. 5. (15 pts) A 1.2crn radius coaxial cable ‘carries a current of 11 = 7.2 mA along its
center wire, and a current [2 = 4.8 mA evenly distributed along its outer conductor.
The two current are in opposite directions (see ﬁgure). Starting from Ampere’s
Law, determine the magnitude of the magnetic ﬁeld at the point P a distance 1.8 cm
from the center of the cable. Justify the steps you take. Side View End View : ~ F [”7 r "v N
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+ 6. (18 pts) Three charges, of magnitude 2.0 C, —2.0 C, and 4.0 C are located as shown in
the diagram. Determine the force acting on the 4 C charge. 7. (5 pts)‘ Three charges of equal magnitude are positioned l,’ \\\
as indicated in the ﬁgure to the right. What is the 1’ \\
electric ﬂux through the spherical surface indicated by ,’ +q —2q “
the dotted circle? (Circle one) _ 1 i . \ l
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0 61/80 261/80 351/80 4q/80 8. (6 pts) Three wires each carry a current I
directly into the page, as shown in the
diagram at right: What is the direction of the magnetic ﬁeld at
the point P equidistant from each of the wires?
(Circle one.) @le—>/\/\0® ..>
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 Spring '08
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