Download Exam I - Physics

Exam 1.00
4 February 2009
College Physics II (PHYS 2020)
Adam Johnston
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Multiple choice: Each question is worth 5 points.
1. The unit known as an "am ere" is used to label a current.
A. volt/meter
2.
Eo joule/second
C. volt/second
Ifan electric field is not zero but is constant in some region of space, what can be said of the potential (voltage, V)
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at pom
A. V must equal zero.
B. V must be
constant.
Or
D. V must be
positive.
must constantly
change.
E. V must be negative.
3. Consider two parallel plates, such as those in a capacitor. The left plate is grounded at 0.00 V and the right
plate is at + 120 V. As one considers the electric field and electric potential at points between the plates,
. f rom Ieft to rIgl
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movmg
A. both E and the
electric potential are
constant.
B. both E and the
electric potential
decrease in
magnitude.
fl.·
~E
.
IS constant b ut
e electric potential
increases in
magnitude
D. E decreases in
magnitude but the
electric potential is
constant .
E. None of
these.
4. Two light bulbs of different resistance are connected in series to a battery. Which of the two will be the
bng!
. htest?.
A. The one closest
B. The one closest
to the '+' side of the to the '-' side of the
battery.
battery.
C. The one with the
least resistance.
~he on~ with the
most reSIstance.
E. More
information is
needed to answer
this question.
5. The familiar circuits below each have the same constant voltage supply, but with different arrangements of
resistors. Rank the currents at oints A, B, and C from hi hest to lowest:
A,B,C
C,A,B
A
A,C,B
B,C,A
c
B
6. A capacitor and a resistor are connected in series to one another and then connected to a battery so that the
ca acitor becomes char ed. The ca acitor will a roach its full char e
A. immediately.
after some
amount of time that
is proportional to
the resistance in the
circuit.
C. after some
amount of time that
is proportional to
the voltage of the
battery.
D. after some
amount of ti'me that
is independent of
the battery and the
resistor.
E. More
information is
needed to answer
this question.
Problems in a parallel universe
C,
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A. [10 points] Below are two parallel plates, as in a capacitor. The plate on the left has a set amount of positive charge,
and the plate on the right has an equal magnitude of negative charge. Draw and label both:
1. An appropriate representation of the electric field between the plates; and,
2. An appropriate representation of the equip( tentialli ~es betw en the p ~
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B. [15 points] If th~ two large, parallel plates are separated by 0.250 m and support an electric field 1.50 x 106 Vim
halfway between them, what is the speed of an electron that is released (from rest) at the negative plate when it arrives at
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C. [10 points] Draw a circuit that has a battery supplying a voltage to a resistor and a capacitor \in gar~llel with one
another. Draw in the placement of an ammeter to measure the current through the resistor, an~olfmeter to measure
the voltage difference across the capacitor.
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Potentially electrifying problems
A. [15 pts.] For the circuit shown, write two (2) unique equations that you
would use to solve for currents 1\ and h, and then show the solution for 1\ in
terms ofR and V. (This is easier than solving for numbers. Note that h, is
the current in two different places, so your kind instructor has already solved
part ofthe problem for you.)
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B. [10 pts.] A typical hair dryer has dissipms4"800 W'ofpower when connected to an electric potential of 120 V.
What is its resistance?
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C. [10 pts.] Imagine that an electron of charge -e is orbiting about a charge of +2e in circular fashion. The charges are
separated a distance of 5.00 x 10'1 1m. How far away from the +2e charge is the voltage zero?
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