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Unformatted text preview: ,._‘ Exam 3 PHYSICS 241 December 3, 2008 Firstname k: = Lastname i 0 IA Section 759 TA”s Name You must start all problems from the equations on‘the sheet.
You must show all work to get full credit for the problem. If you need more space, you may use the back of the sheet. If you do so. make sure that .. you put an arrow indicating that. Do not get hung up on algebra. It is only worth a small fraction of the points. Do not spend too much time on any one problem. The point values are listed for each
question so you can make efﬁcient use of your time. Some problems may involve several steps. Even if you can’t ﬁgure out all of them, write
down what you do know. You can also explain in words what to do. For example ”If I could
ﬁnd the time t (which I don’t know how to do) I would use it in this equation to ﬁnd blank. ..”. The phrase “in terms of whatever variables...” certainly implies that you must use variables
given in the statement of the problem. You cannot have variables in the ﬁnal answer which
depend upon each other. For example, you can’t have a velocity v in your ﬁnal answer if it
can be expressed in terms of the time t which you also have in the ﬁnal answer. Lastly, you
answer can obviously include any needed constants. Please box your answers. Good Luck. 1a: Four inﬁnite straight currents are arranged at the corners of a perfect square. Deteri
mine/explain the direction of the magnetic ﬁeld exactly at the center of the square. 10
points. 0 as; X 2 a mm as Mme)
gag are as Clﬂmmn go "Hug mil" $56,th 'x b: If a proton were travelling to the left at the center of the square, what wou be the
direction of the force on it? 5 points. ‘ L7 RH'R 'ﬁ‘é home is 'mwomdls 63) Page 2 __ Page 3 ‘ i
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Page 6 ___ Page 7 Total /100 2a: A single loop of area A is in a region of space with a magnetic field which is pictured
here at time zero. In general, the magnetic ﬁeld is described by B(t) 2 Bo cos wt. Assuming
the loop has a resistance R, determine the earliest time at which the power delivered to the
loop is a maximum. 15 points. b: What is the average power delivered to the loop over avery long time? Explain/ calculate.
(This should not require much work.) 10 points. x X X X61)€;_U§E=elf~i—:(8Bw§”l—A) x X all
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X X X X = —~ BOAuJ ~S£noitj " AEovJSlnbJ 3: There are two inﬁnite surface currents [below left) and both are described by a linear current density I? = K053. If needed, you may assume that they are a distance D apart
and that the xy plane is exactly halfway between them. Determine the magnetic ﬁeld ev—
erywhere in Space. 20 points. W WWW: m Rem tread Charis r”? ahoud 6mg
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1611;?“ i2? ﬁx, Icf+ HvoujLu ‘hhé [10le > 1012“} =,(Zf 1 4: A straight nite current exists as shown. It has a steadily increasing current. There are ‘
four rectangular loops( (of size L by H) near it. Note that loop number 4 IS perpendicular to the other three so you are seeing only one edge of it. Rank the magnitude of the induced emf in each loop. Explain your answer. In the loop with the largest 61an you should also fully explain the direction of the induced current. 17 points. M (Ha ﬂux '15 increafi'ng FmoorQS‘ Se “ch 40*
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ﬂxe 1111911659 mm 33 C00 Loy The KW? 5: You have a series RLC’ circuit that is primarily capacitive (X0 > X L and X0 > R). The angular frequency of the voltage source in the circuit is slightly decreased. What hap
pens to the power delivered to the resistor? Explain. 15 points P = _L l? ‘ into:
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Jro “Tr ‘me 1L alrdaﬂy wag, Can you prove Hﬁs7 6: The switch is connected at position A for a time T. It is then switched to position B
and left there for a long time. Graph the current through the resistor as a function of time.
You do not have to explain your graph. If the graph is correct, you will receive full credit.
However, explaining your graph may help with partial credit. 15 points. C ﬁx: intact; or 'Forcff I Kilo” "'anC’RSP ;
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