Download Test 3

Physics 25
Test 3
April 26, 2012
Key
Name - - - - - 1 - - - - - - - - - - - ­
I
Leave your answer in terms of
1.
(£0' flo' Jr)
treated as numbers without units.
A pair of parallel conducting rails lie in a uniform magnetic field B= 3T pointing into the
page. The rails are a distance of 4 m apart and a resistance R= 12 ohms is connected to
them. A bar lying across the rails is being pulled to the right with a constant speed v= 7 mls.
(a) What is the induced Emf?
(b) How much current is flowing through the resistor?
(c) Is the current flowing clockwise or counterclockwise?
X
B
L
R
v
~
><
¢B -
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vi p~
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tit
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-- ~) (l/)(7)
b)
7
c:)
,s
~
wi se..
2.
A Gaussian surface in the shape of a right circular cylinder with end caps has a radius of 3
m and a length of 5 m. Through one end there is an inward flux of 25 Wb. At the other end
there is a uniform magnetic field of
~ T, normal to the surface and directed outward.
1[
a.
What is the magnitude of the net magnetic flux through the curved surface?
b.
What is the direction of the flux (inward or outward)?
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¢~ +-
¢tk ¢,up
=
~~
- :JS
f3A
:.
~
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¢T1
~
0
wla
B 7T k 7..
(J J(rr) (3)
z..
:::.
1/ W b
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+- 3t Wb
3.
A parallel plate capacitor has circular plates of radius 2 m and spacing 1 mm. A uniform
electric field is established between the plates. The electric field is decreasing at the rate of
6
- - - V/(m s).
).10 &0
a. What is the magnitude of the displacement current 4 m from the center of the plate?
b. What is the magnitude of the magnetic field 4 m from the center of the plate?
c. What is the direction of the magnetic field (clockwise or counterclockwise)?
E
X
2m
a) /lJ 1= £0
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rtt
~)
z.
==
~ rr(~)
:J Lj
-
b)
B -
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)10
2rr12...
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fi
--
rr
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elf )
3T
~
)J~
f+h\f
4.
A point source of light is 25.J3 feet under the surface of a liquid which has an index of
refraction of 2. Find the radius of the circle at the surface through which light emerges from
the liquid.
tv,
~
. fJ
IJ~
~
~
~
90°
fUMe- ­
.-L
~b ::.
8
::
J.
30
()
+tW\ e R.=
25 {i
;15.G
~ 30
(tI)
5.
An optical instrument (01) is known to be either a thin lens or mirror. It is experimentally
found that, if an 0 bject is placed far away in front of the 01, a virtual image is formed
behind the 01.
a.
Is this 01 a lens or a mirror? Is this 01 convex or concave?
m/ff'o r
b.
If the image is
~
3
Co tJV-f X
as large as the object, what is the magnification (magnitude and sign)?
...L
M ~
c.
If the object is 30 inches from the 01, how far is the image from the OI?
.f~
(Y/::O
J:...
- f
so
C
d.
.3
f
-
<:'
if --
What is the focal length of this OI?
.1­
...L
..L
+
t
-l_/0
J.-
30
..L
-r
30
t
+
-
f
..L
30
L
::
-f
-­
.L­
.p­
}J
//
- /0
6.
Young's double slit experiment is performed with blue-green light of wavelength 500 nm.
If the slits are 2.5 mm apart and the viewing screen is 10m away, what is the distance
rd
between the center bright spot and the 3 bright spot from the center?
('/'';
J
)
~~
-rlt"'}
f
__
\~--..;...,,;e
\
3
s
-...p
L, ID WI
--s
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(V'\
(~)
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(m
X J0 - q )
(J 0
)
s ­
7:-5"
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