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AP Physics – Worksheet #1: Chapter 17
Electric Forces and Fields
Coulomb’s Law, Electric field of a point charge
1. Two point charges are separated by 2 m, as shown.
a) What is the magnitude and direction of the force that the 400
µC charge exerts on the -200 µC charge?
Figure 1
b) What is the magnitude and direction of the force that the -200 µC charge exerts on the 400 µC charge?
c) If as is shown in Fig. 2 the -200 µC charge is moved to point
A what is the magnitude and direction of the force that the 400 µC
charge exerts on the -200 µC charge?
Figure 2
2. As is shown in Fig. 3 suppose a third charge of 100 µC is added to the original configuration and positioned
at point D. What is the magnitude and direction of the force on this charge? Illustrate the superposition
principle by drawing vectors approximately to scale representing each of the two forces and the vector sum of
these forces.
Figure 3
3. Suppose a third charge of 100 µC is added to the original
arrangement of the charges and positioned at point A as shown
in Fig. 4 . What is the magnitude and direction of the force on
this charge? Illustrate the superposition principle by drawing
vectors approximately to scale representing each of the two
forces and the vector sum of these forces.
Figure 4
4. What is the magnitude and direction of the electric field at
the point A due to the two charges in the original arrangement
of the two charges as shown in Fig. 5? Illustrate the
superposition principle by drawing vectors approximately to
scale representing each of the two electric fields and the vector
sum of these fields.
Figure 5
5. Draw a sketch of the electric field lines for the two charges in the original arrangement in Fig. 1.
For extra credit answer question 6.
Figure 6
6. In Figure 6 pick a point P that is not on the line containing points B, C and D.
a) Draw two vectors to represent the electric field at point P produced by each of the two charges in the
original arrangement in Fig. 1.
b) Explain from this why the electric field cannot be zero for points off the line containing points B, C and D.
c) Explain similarly why the electric field cannot be zero on the line containing the charges at points to the east
of the -200 µC charge.
d) Where on the line of the two charges is the electric field zero?