Coulomb’s law & electric fields worksheet with answers

Free printable Coulomb’s law & electric fields worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy
+q₁+q₂r

Two point charges repel each other with a force of 4 N. The first charge is doubled and the distance between the charges is halved. Find the new force F′.

F = 4 Nq₁′ = 2·q₁r′ = 0.5·r
F′ = N
2.Easy
++8 µC−−4 µCr = ?

Point charges of +8 µC and −4 µC exert a force of 8 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = −4 µCF = 8 N
r = cm
3.Medium
++8 µC++2 µCE = 030 cm

Charges of +8 µC and +2 µC are 30 cm apart. At what distance x from the +8 µC charge, on the line between them, is the electric field zero?

q1 = +8 µCq2 = +2 µCd = 30 cm
x = cm
4.Medium
++5 µC−−4 µCr = 30 cm

Two identical small metal spheres carry charges of +5 µC and −4 µC. They are touched together and then put back 30 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +5 µCq2 = −4 µCr = 30 cm
F = N
5.Hard
8 cm5 cm+q1​ = +8 µC+q3​ = +3 µC+q2​ = +10 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 3 µC is at the right-angle corner, q₁ = 8 µC is 8 cm from it along one side and q₂ = 10 µC is 5 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 8 µCq2 = 10 µCq3 = 3 µCr13 = 8 cmr23 = 5 cm
F = N
6.Hard
4 cm4 cm+q1​ = +8 µC+q3​ = +5 µC+q2​ = +8 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 5 µC is at the right-angle corner, q₁ = 8 µC is 4 cm from it along one side and q₂ = 8 µC is 4 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 8 µCq2 = 8 µCq3 = 5 µCr13 = 4 cmr23 = 4 cm
F = N

Answer key

  1. 1. F′ = 32 N
  2. 2. r = 18.96 cm
  3. 3. x = 20 cm
  4. 4. F = 0.02497 N
  5. 5. F = 113 N
  6. 6. F = 317.8 N

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