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
++4 µC++8 µCr = ?

Point charges of +4 µC and +8 µC exert a force of 0.5 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +4 µCq2 = +8 µCF = 0.5 N
r = cm
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 42 N. The first charge is doubled and the distance between the charges is made four times as large. Find the new force F′.

F = 42 Nq₁′ = 2·q₁r′ = 4·r
F′ = N
3.Medium
−−6 µC++5 µCr = 20 cm

Two identical small metal spheres carry charges of −6 µC and +5 µC. They are touched together and then put back 20 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −6 µCq2 = +5 µCr = 20 cm
F = N
4.Medium
++6 µC++8 µCE = 080 cm

Charges of +6 µC and +8 µC are 80 cm apart. At what distance x from the +6 µC charge, on the line between them, is the electric field zero?

q1 = +6 µCq2 = +8 µCd = 80 cm
x = cm
5.Hard
4 cm4 cm+q1​ = +10 µC+q3​ = +4 µC+q2​ = +4 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 4 µC is at the right-angle corner, q₁ = 10 µC is 4 cm from it along one side and q₂ = 4 µC is 4 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 10 µCq2 = 4 µCq3 = 4 µCr13 = 4 cmr23 = 4 cm
F = N
6.Hard
6 cm5 cm+q1​ = +4 µC+q3​ = +3 µC+q2​ = +6 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 3 µC is at the right-angle corner, q₁ = 4 µC is 6 cm from it along one side and q₂ = 6 µC is 5 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 4 µCq2 = 6 µCq3 = 3 µCr13 = 6 cmr23 = 5 cm
F = N

Answer key

  1. 1. r = 75.85 cm
  2. 2. F′ = 5.25 N
  3. 3. F = 0.05619 N
  4. 4. x = 37.13 cm
  5. 5. F = 242.1 N
  6. 6. F = 71.33 N

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