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Physics
2020
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Summer 2016
Richard Ingebretsen
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Exam 3
Name:
UNID:
TA: 4~E^M-A •
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In lecture this week, Kevin proposed a simple method of magnetizing a screwdriver. This can be extremely
useful so that metallic screws stay with the screwdriver instead of falling and rolling into hard-to-reach places
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that was
acts the
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a charged
through
a magnetic
field is proportional to several variables.
What
thatparticle
Kevin moving
proposed,
and what
is it called?
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i !A^>^x^6'6>i,HBriefly define what a transformer is m your ow^words, and give an example of onp:
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C.
D.
Determine the direction (clockwise or counterclockwise) of
the induced current in the loop for each case shown in the
figure (labelled (a) through (f)). Expressjtll your answers as
- f\
scft> \.v*n viewed from the side of the looplhat has the magnet. No
induced ClITTeht is also a possible answer.
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E.
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What is the time constant for the RC circuit in a common flash attachment of a disposable camera. (Assume that
thg resistor is about 1 fcQ and the capacitor is about 100 uF.)
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Physics 2020
Summer 2016
Richard In«ebretsen
Exam 3
Name:
UNID:
TA: ELto
A.
2
You have a 5.0 uF capacitor and a collection of resistors and batteries available. Build a complete RC circuit that
puts a maximum charge of 120 \iC on the capacitor, and also charges the capacitor with 50% of its maximum
charge in a time of 13.86 us. The batteries you have available have voltages of 6 V, 12V, 18V and 24 V. You
have one 1 Cl resistor, one 2 Q resistor, one 5 Cl resistor and two 8 Q resistors.
oo.
B.
' 'he drawing shows the circular paths of an electron and a proton. These
particles have the same charge magnitudes, but the proton is more massive.
They travel at the same speed in a uniform magnetic field B, which is
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directed into the page everywhere. Which particle follows the larger circle,
and does it travel clockwise or counterclockwise?
H (into page)
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A magnetic field of 45 uTTs^affected straight cfowri, perpendicular to the plane of a circular coil of wire that is
made up of 200 turns, a constant resistance of 25 Q and has a radius of 10 cm. If the coil is stretched in a time of
16 ms to a new radius of 20 cm, calculate the magnitude of the induced current in the coil during the stretching
process.
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Physics 2020
Summer 201 6
Richard Ingebretsen B
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Exam 3
Name:
UNID:
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A length of copper wire is formed into a square loop with 50 turns.
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The loop is free to turn about a frictionless axis that lies in the plane
of the loop and passes through its center. Each side of the loop is^.OO
cm long, and the moment of inertia of the loop about the axis or
rotation is 4.00 x 10~6 kg • m2. The loop lies in a region where there
is a uniform magnetic field of magnitude 1.50xlO~ 2 T that is
perpendicular to the rotation axis of the loop. The current in the loop
is 0.500 A. Find the angular acceleration of the loop (magnitude and
direction) when the loop is released from rest from the orientation
, shown
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An electron has a kinetic energy of 2.0 x 10 17 ]. It moves on a circular path that is perpendicular to a uniform
magnetic field of magnitude 5.3 x 10~5 T. Determine the radius of the path.
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.C.
D.
Right or wrong? The root mean square value for voltage is more useful than the average value because the
average value is often zero.
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Calculate the frequency of blue light, which has,a wavelength of 470 nm.
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Physics 2020
Summer 2016
Richard Ingebretscn
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Exam 3
Name:
UNID:
TA: &YA.Y
A.
A horizontal wire is hung from the ceiling of a room by two massless
strings. The wire has a length •£ and a mass m. A uniform magnetic field of
magnitude B is directed from the ceiling to the floor. When a current /
exists in the wire, the wire swings upward and, at equilibrium, makes an
angle 0 with respect to the vertical, as shown. Find the following in terms
of f , m, B, g and /:
1.
2.
B.
4
The angle 0
The tension in each of the two strings
A coaxial cable consists of a solid inner conductor of radius/?;,
surrounded by a concentric outer conducting shell of radius /?(,.
Insulating material fills the space between the conductors. The
inner conductor carries current to the right, and the outer
conductor carries the same current to the left down the outer
surface of the cable, as shown in the figure. Using Ampere's
law, derive an expression for the magnetic field in three
separate regions of space: inside the inner conductor (r < fy),
between the two conductors (fy < r < R0), and outside of the
outer conductor (r > R0).
(Use the following as necessary: ^QJ i, f, and Rj. Do not substitute any values or variables for ^o-)
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