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Unformatted text preview: Quiz 4 Solutions These solutions are written for version A. The questions for versions B and C are related as
follows: A B C
1 —> 2 1
2 —> 4 3
3 —> 6 5
4 —> 8 7
5 —> 10 9
6 —> 1 2
7 —> 3 4
8 —> 5 6
9 —> 7 8
10 —> 9 10 1. The electron moves parallel to the magnetic ﬁeld, so 6 = 0, thus F = (1113 sin(6) becomes
F = qu sin(0) = 0. 2. As with 1., we have theta = 0 such that F = BIlsin(6) = 0, 3. Using our right hand rule, we can ﬁnd the direction of the magnetic ﬁeld due to wire 1 at
wire 2. Then, using our right hand rule for the force, we ﬁnd that the current of wire 2 being
opposite in direction to the current of wire 1 gives us a repulsive force. 4 Usng § = % we get (0.8%,) = (4”X10_7T2,132/2§31§‘;"0A)(10A). This gives us F = 3.2x105 N,
(a) t
N 0 = #00041” = 2x10’3 T, (a). 5' B : 271'1’ 27r(1m) 6. Using (1)3 2 BA cos(6). Here, our area lies perpendicular to the magnetic ﬁeld, thus 6 = 0 between the magnetic ﬁeld and the normal of the area (ie, the line that comes out perpendicular
to the area). This gives us <I>B = (4.5 T)(0.10 m2) = .45 Tm2, (b). 7. The current is held constant in the primary wire, thus there is no changing ﬁux. Without
a changing flux, there can be no induced current, so the answer is zero, 8. To ﬁnd the induced current, we must ﬁrst ﬁnd the induced EMF. Where 5 = —NAAitB.
Using (1)3 2 BA cos(6), we get ABAcos(0)
= _N—
6 At
2 IR
_ ABAcos(6)
2‘1 — _NA—tR
_ 4(25—10mT)(200cm2) (5ms)(5.09)
Which gives us I = 48 mA, 9. When the magnet ﬁrst enters the loop, the induced current creates a magnetic ﬁeld to
oppose the magnet. Once the center of the magnet passes through the loop, the loop’s current
now creates a magnetic ﬁeld to try to attract the magnet. Remember that induced current resists
change. Thus the current would be induced to create a magnetic field pointing downwards (or
into the page as viewed from above). This would be caused by a clockwise moving current (as viewed from above), (a). 10. A generator is a moving piece of wire that creates a current; thus, mechanical energy is
converted into electric energy, (a). ...
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 Spring '07
 Onuich
 Physics, Magnetism

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