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Physics 131 Exam 1 Topics and Study Problems
Spring 2022
Cuyamaca College
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Topics to Study:
1. Coulomb’s Law
2. Static electricity
3. Electric fields and action at a distance
4. Electric potential
5. Conservation of energy in the electric world
6. Resistivity and Resistance
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1. Due to negative ions floating in the atmosphere, the earth has a natural electric field near
its surface equal to about 150 N/C. This field points directly towards the ground. What
charge in coulombs would a 80-kg person need to have in order to balance his or her
weight with the force exerted by the electric field? Hint: Draw a picture/freebody
diagram!
a.
b.
c.
d.
2.5C
5.2C
3.4C
4.3C
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2. If both charges q1 and q2 in the
drawing are positive, what would
be the direction of the net electric
field at points A, B, and C
respectively? Use vector arrows to
prove your answer.
a.
b.
c.
d.
e.
Left, up, down.
Right, down, up.
Right, zero, right.
Zero, up, down.
Up, zero, up.
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3. Find the electric potential one micrometer away from a nitrogen nucleus?
A) 0.01V
B) 0.002V
C) 0.0003V
D) 0.00004V
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4. As you know, neurons are essentially the wires in the body that send electrical impulses
so that signals can be sent throughout the body. This electric signal happens when ions
suddenly rush into and then out of the axon of the neuron. Measurements have shown that
during the inflow part of this cycle, approximately 6×1011 Na+ ions rush in per meter.
(Each single positive ion has the charge of one proton). How many coulombs of charge
enter a 2-cm length of the axon during this process?
a.
b.
c.
d.
-6×1011 C
4×10-11 C
-4.6×10-6 C
1.9×10-9 C
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5. After clothes tumble in the dryer, there is a static coulomb force that causes them to cling
together after you pull them out. What charging method is most responsible for the
charge imbalance that causes this electric force. Use both pictures and words to explain.
a.
b.
c.
d.
Charging by induction
Charging by contact
Charging by friction
None of the above
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6. Two identical positive charges are placed near each other. At the point halfway between
the two positive charges, what best describes the electric field and electric potential at
that point. Explain your answer using pictures and words.
a.
b.
c.
d.
The electric field is zero and the potential is positive.
The electric field is zero and the potential is zero.
The electric field is not zero and the potential is positive.
The electric field is not zero and the potential is zero.
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7. A bolt of lightning can strike with a current of 25,000 A for a whopping 40 μs. How
many electrons are transferred to the ground during such a bolt?
a. 6.25×1018 Electrons
b. 8.25×1016 Electrons
c. 2.25×10-18 Electrons
d. 4.25×10-18 Electrons
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8. What is the resistance of a 1m long tungsten wire 1mm in diameter? The resistivity of
Tungsten at room temperature is 5.6×10-8 Ohm-meters.
a.
b.
c.
d.
0.7 Ohms
0.07 Ohms
0.4 Ohms
0.04 Ohms
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