WE 3301 Midterm Problems
1) Draw the schematic circuit for the pictorial diagram below:
2) An initially neutral body has 1.7 μC of negative charge removed. Later, 18.7 x 1011 electrons
are added. What is the body’s final charge?
3) Two charges of 1 C each are placed one meter apart. Calculate the electrostatic force between
them. Is the force attractive or repulsive?
4) 100 J of energy are needed in order to move a charge of 5 C from one point A to another point
B. What is the voltage between those two points?
5) If a charge amount of 1680 C passes through the imaginary plane as shown of the figure below
during 4 minutes, what is the electric current at the lamp?
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6) Batteries run down under use. The capacity of a battery is specified in ampere-hours (Ah).
The ampere-hour rating of a battery is equal to the product of its current drain times the
length of time that one can expect to draw the specified current before the battery is gone.
Calculate the service capacity of an AA battery with a current drain of 3 mA and a service life
of 450 h.
7) Draw the schematics for the following two battery connections. Can you explain the value of
the output voltage in the series connection? What is the output voltage in the parallel one
Series connection
Parallel connection
8) What is wrong about this picture?
I =5 A
9) A string of 24 light bulbs is connected to a 120 V supply as shown in the picture below. Each
bulb has a resistance of 25 Ω. Calculate the electric current.
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10) Determine the magnitude and correct direction of currents I3 and I5 for the network of the
following figure:
11) Find the magnitudes of the unknown currents for the following network:
12) A parallel-plate capacitor with air dielectric has a capacitance of 12 pF. What is the
capacitance of a capacitor that has the following properties:
a) The same separation and dielectric but five times the plate area?
b) The same dielectric but four times the area and one-fifth the plate spacing?
c) A dry paper dielectric, six times the plate are and twice the plate spacing? Dry paper has a
dielectric constant 2.2 times larger than air.
13) If the magnetic flux through a 400-turn coil changes steadily from 2 Wb to 10 Wb in one
second, what is the induced voltage?
14) If the current through a 10 mH inductance changes at a rate of 2000 A/s, what is the induced
voltage?
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15) Using the result for the last exercise on Faraday’s law
𝑉 = −𝑁
𝑑𝛷
𝑑𝑡
= 2𝜋𝑓𝑁𝑎𝑏𝐵𝑠𝑖𝑛(2𝜋𝑓𝑡)
Can you design a loop for the previous exercise that may produce 120 V with f = 60 Hz?
Use a uniform magnetic field of 0.5 T.
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