Physics 2145 Test 1 Preparation homework
1. Three charges are arranged as shown.
a) Draw the forces on Q which are
exerted by q1 and q2.
b) Calculate the magnitudes of the forces
that q1 and q2 exerts on Q, respectively.
c) Calculate magnitude of the net force,
FNET, on Q due to q1 and q2.
d) Calculate the angle between FNET and
the positive x-axis.
q2= -10.0μC
q1 = +7.50μC
20cm
22cm
300
Q= +5.55μC
2. Two identical positive charges of magnitude q are located on the y-axis a distance a from the
origin. Point B is located on the x-axis,
a distance b from the origin.
q
a) What is the direction of the electric
field created by these two charges at the
a
origin? (indicate in the diagram.)
b
b) At point B, sketch the electric fields
due to each of the charges and the net
electric field.
c) Calculate the magnitudes of the
electric fields at B due to each of the
charges.
d) Calculate the net electric field at B.
e) Calculate the net electric potential at point B.
B
a
q
x
3. An electron starts from rest at the negative
plate which has a potential Vi = 0. The
electron is accelerated towards the positive
plate which is at a potential Vf with respect
to the upper plate.
a) Is Vf < Vi or Vf > Vi ?
b) What is the initial potential energy of the
electron before it is released?
c) What is the final potential energy of the
electron as it reached the positive plate (at
the tip of the arrowhead in the diagram)?
d) In terms of Vf , me and e, what is the final
velocity of the electron?
-----------------------------Vi=0
V=Vf
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4. In the Physics 26 laboratory, a student makes a plane parallel plate capacitor by taking two
pieces of aluminum foil and inserting a sheet of paper in between the two pieces of foil. The two
pieces of aluminum foil are 30 cm by 30 cm. and the paper is 0.10 mm thick and has a dielectric
constant K = 3.70.
a) What is the capacitance of this capacitor?
b) When the student connects this capacitor to a power supply and sets the voltage to V = 150 V,
how much charge is stored on the capacitor?
5. Find the equivalent capacitance between points a and b. How much charge is stored in the
capacitor configuration if a potential difference ΔV=10V is applied between a and b?
8μF
a
12μF
b
24μF