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Electric Forces & Charges (Coulomb’s Law) Chapter 25 Electric Forces & Charges (Coulomb’s Law)
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Announcements Homework for tomorrow…
(Ch. 25, CQ 12, Probs. 18 & 40)
Office hours…MWF 12:30-1:30 pm TR 9-10 am
Tutorial Learning Center (TLC) hours:??
Chapter 25
Electric Forces & Charges(Coulomb’s Law)
where
Notice: Mass is always positive. Gravity is always attractive.
Newton’s Law of Gravitation, revisited..
G6.6710 11 N m2
kg2
m1
m2
r
where
Notice: Charges can be positive or negative. Force can be attractive or repulsive.
Coulomb’s Law..
q1
q2
r
Coulomb’s Law - restrictionscharges must be small compared to their
separation (“point-like”)
OK
Not OK
Quiz Question 1 Two uniformly charged spheres are firmly fastened to and
electrically insulated from frictionless pucks on an air table. The charge on sphere 2 is three times the charge of sphere 1.
Which force diagram correctly shows the magnitude and direction of the electrostatic force on each object?
Coulomb’s Law and Superposition Q: What is the ?
q1
q2
q3
Coulomb’s Law and Superposition Q: What is the ?
A:
q1
q2
q3
Quiz Question 2 Two protons (p1 and p2) and an electron (e)
lie on a straight line as shown. The direction of the net force on p1 , p2 , and e, respectively, are:
1. left, right, left2. left, right, right3. right, left, left4. right, left, right5. right, right, left
p1 p2 e
Prob. 25.16What is the net electric force on charge A in Figure EX25.16?
Prob. 25.37What is the force F on the 5.0 nC charge in Figure P25.37?
Give your answer as a magnitude and an angle measured cw or ccw (specify which) from the + x-axis.