Download AP Physics – Worksheet #2: Chapter 18 Electric Forc

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AP Physics – Worksheet #2: Chapter 18
Electric Force, Fields, Potential Energy and Potential
Potential energy of interaction of two point charges
PE =
k e q1 q 2
r
k e =8.99×109 Nm 2 /C 2
ke q
Potential of a point charge V =
Potential in a uniform electric field E in the +x direction V = -E x
r
Change in potential energy of a point charge in an electric potential field  PE=q  V
Capacitance in farads C = Q/V
Capacitance of a parallel plate capacitor C = ε0 A / d
The permitivity of free space is ε0 = 1 / (4 π kC) = 8.85x10-12 F/m
1
Q2
2
Energy stored in a capacitor W = C  V =
2
2C
Coulomb constant
1. A point charge of +0.80 μC is located at the origin. What is the electric potential at the point x = 40 cm?
A point charge of +0.80 μC is located at the origin, and a second point charge of −4 μC is at x = 40 cm. Answer
the following questions:
2. What is the electric potential energy stored in the two charge system? Explain the significance of the sign
on your answer.
3. What is the electric potential due to these two charges at the point x = 100 cm?
4. At what point on the x-axis is the electric potential due to these two charges equal to zero?
5. If these two charges on positioned on a circle of radius 80 cm what is the electric potential at the circle’s
center ? Does your answer depend on the particular place on the circle that the charges are placed? Explain
your answer.
Two parallel plates each with an area of 0.080 m2 are separated by a distance of 5 cm. The plates are connected
to a 12-V battery as shown in Fig. 1.
6. Determine the Electric Field between the plates (assume the electric field between the plates is uniform).
What direction is the electric field?
7. How much charge is stored on the capacitor?
8. How much energy is stored in the capacitor?
If a proton (charge = 1.60×10-19 C, mass = 1.67×10-27 kg) is released at the positively charged plate, it will be
accelerated towards the negative plate.
9. What is the change in potential energy of the proton from its starting position (positive plate) to its ending
position (hitting the negative plate)?
10. Knowing that energy is conserved, and thus a decrease in potential energy results in an increase in kinetic
energy, what is the final kinetic energy of the proton just before it hits the negatively charged plate after it is
released at rest?
11. What is the speed of the proton just before it hits the negatively charged plate?