Summary

• Electric charges
• Coulomb's law
• Electric fields

• Electric field
• lines of force
1. Lines point in direction of force
2. Number of lines proportional to the charge
3. Line density indicates field strength
• lines of force applet
• 3-d vector fields applet

• Electric field video
Example #1
Example #2
Example #3



• continuous charge distributions
• line charge λ
• surface charge σ
• volume charge ρ_e




• Practice:
  Try this additional example:
Example #4



• Prepare:
  Read textbook sections 22.6, 23.1, and 23.2 before the next lecture

pop4 19.qq.5
Rank the magnitudes of the electric field at points A, B, and C in the figure.
1. C > B > A
2. B = A > C
3. C > A = B
4. A > B > C
5. B > A > C
Answer















gc6 16.32
The electric field midway between two equal but opposite point charges is 745 N/C, and the distance between the charges is 16.0 cm. What is the magnitude of the charge on each?
A. 3.31×10⁻⁹ C
B. 2.65×10⁻¹⁰ C
C. 4.14×10⁻⁶ C
D. 3.02×10⁸ C
Answer















sb5 23.44
What field is required to stop electrons having energy 1.60×10⁻¹⁷ J in a distance of 10.0 cm?
A. 1.0 N/C
B. 10 N/C
C. 100 N/C
D. 1000 N/C
Answer















Walker5e EYU 19.5
The electric field lines for a system of two charges is shown below. Which of the following could be the correct charges 1 and 2?
A. q₁ = +32 µC,    q₂ = −16 µC
B. q₁ = −32 µC,    q₂ = +16 µC
C. q₁ = −16 µC,    q₂ = +32 µC
D. q₁ = −16 µC,    q₂ = −32 µC
Answer

























 



4. A > B > C

The field is strongest where the lines are most closely spaced.




















 



B. 2.65×10⁻¹⁰ C






















 



D. 1000 N/C

















 



B. q₁ = −32 µC,    q₂ = +16 µC

The electric field lines converge toward charge 1 and away from 2, which means charge 1 is negative and charge 2 is positive. Because there are twice as many lines connected to charge 1 as there are connected to charge 2, the magnitude of q₁ must be twice the magnitude of q₂.