Exam1a Solutions

1. A proton is accelerated by a constant electric field of magnitude 100 N/C. Using
,the equations of motion with constant acceleration find the proton's speed after
1.OO x 10" s, assuming it starts from rest.
I Comment [ASl]:
Correct answer
2. An electron is sent at high speed toward a gold nucleus (charge +79e). What is
the electrical force acting on the electron when it is 3.0 x 10-l4 m away from the
gold nucleus? (e = 1.6 x 10-l9 C, k, = 8.99 x 1o9 N.rn2/c2)
F = k pg/
(comment [AS2]: Correct answer
3. A square loop with sides of length 50 cm is placed in a uniform electric field such
that the electric field makes an angle of 45" to the perpendicular direction of the
loop. If the electric field strength is 500 N/C what is the electric flux through the
I Comment [AS3]:
Correct answer
4. A charge of +2 C is at the origin. When charge Q is placed at 2 m along the
positive x axis, theb-dat
2 m along the negative x axis becomes zero.
What is the value of Q?
I - -2m
Comment [AS4]: Correct answer
5. What is the equivalent capacitance between points and b? All capacitors are 1.0
h m m e n t [ASS]: Correct answer
Comment [AS6]: Correct answer
6. A "sandwich" is constructed of two flat pieces of metal (2.00 cm on a side) with a
2.00-mm-thick piece of a dielectric called Rutile ( K = 100) in between them.
What is the capacitance? (a = 8.85 x 10-l2 ~ ~ h l - r n ~ ) .
7. A 0.25-pF capacitor is connected to a 400-V battery. Find the charge on the
Comment CAS7I: Correct answer
Two capacitors Cl = 20-pF and C2= 5-pF are connected in series and charged
with a 100-V power supply. What is the total energy stored in the two capacitors?
9. A flashlight bulb operating at a voltage of 4.5 V has a resistance of 8.0 a. How
many electrons pass through the bulb filament per second (e = 1.6 x 10-lgC)?
10. A metallic conductor has a resistivity of 19 x
R-m. What is the resistance of
a piece of this conductor that is 30 m long and has a diameter of 2 mm?
~ * * c c = Q * O O 2 r c \
[ASlO]: Correct answer
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11. 150, 0.5-W decorative lightbulbs are connected in parallel on a string of lights
which is connected to a 120-V source. What current is delivered to the lights by
the source?
12. A 20-0 platinum wire at 20°C with a temperature coefficient of resistivity of 3.9
x 10" ("c)-' will have what resistance at 100°C?
d. 28 R
e. 32 R
= Odds4
Comment [AS12]: Correct answer
, K = 20°c , T= lodoc