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
++3 µC++5 µCr = 4 cm

Two point charges of +3 µC and +5 µC are 4 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = +5 µCr = 4 cm
F = N
2.Easy
++8 µC−−8 µCr = ?

Point charges of +8 µC and −8 µC exert a force of 1 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 = −8 µCF = 1 N
r = cm
3.Medium
++1 µC++3 µCE = 020 cm

Charges of +1 µC and +3 µC are 20 cm apart. At what distance x from the +1 µC charge, on the line between them, is the electric field zero?

q1 = +1 µCq2 = +3 µCd = 20 cm
x = cm
4.Medium
++1 µC++5 µCP20 cm

A charge of +1 µC and a charge of +5 µC are 20 cm apart. Point P lies on the line between them, 5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +1 µCq2 = +5 µCr1 = 5 cmr2 = 15 cm
E = N/C
5.Hard
10 cm5 cm+q1​ = +2 µC+q3​ = +6 µC+q2​ = +1 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 6 µC is at the right-angle corner, q₁ = 2 µC is 10 cm from it along one side and q₂ = 1 µC is 5 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 2 µCq2 = 1 µCq3 = 6 µCr13 = 10 cmr23 = 5 cm
F = N
6.Hard
6 cm10 cm+q1​ = +4 µC+q3​ = +4 µC+q2​ = +3 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 4 µC is at the right-angle corner, q₁ = 4 µC is 6 cm from it along one side and q₂ = 3 µC is 10 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 4 µCq2 = 3 µCq3 = 4 µCr13 = 6 cmr23 = 10 cm
F = N

Answer key

  1. 1. F = 84.28 N
  2. 2. r = 75.85 cm
  3. 3. x = 7.321 cm
  4. 4. E = 1.598 × 10⁶ N/C
  5. 5. F = 24.12 N
  6. 6. F = 41.39 N

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