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
++8 µC−−10 µCr = 30 cm

Two point charges of +8 µC and −10 µC are 30 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = −10 µCr = 30 cm
F = N
2.Easy
++1 µC++5 µCr = ?

Point charges of +1 µC and +5 µC exert a force of 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 = +1 µCq2 = +5 µCF = 5 N
r = cm
3.Medium
++4 µC−−4 µCP20 cm

A charge of +4 µC and a charge of −4 µC are 20 cm apart. Point P lies on the line between them, 15 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +4 µCq2 = −4 µCr1 = 15 cmr2 = 5 cm
E = N/C
4.Medium
++3 µC−−4 µCP30 cm

A charge of +3 µC and a charge of −4 µC are 30 cm apart. Point P lies on the line between them, 22.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +3 µCq2 = −4 µCr1 = 22.5 cmr2 = 7.5 cm
E = N/C
5.Hard
10 cm8 cm+q1​ = +2 µC+q3​ = +8 µC+q2​ = +8 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 8 µC is at the right-angle corner, q₁ = 2 µC is 10 cm from it along one side and q₂ = 8 µC is 8 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 2 µCq2 = 8 µCq3 = 8 µCr13 = 10 cmr23 = 8 cm
F = N
6.Hard
4 cm5 cm+q1​ = +4 µC+q3​ = +2 µC+q2​ = +1 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 2 µC is at the right-angle corner, q₁ = 4 µC is 4 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 = 4 µCq2 = 1 µCq3 = 2 µCr13 = 4 cmr23 = 5 cm
F = N

Answer key

  1. 1. F = 7.991 N
  2. 2. r = 9.482 cm
  3. 3. E = 1.598 × 10⁷ N/C
  4. 4. E = 6.926 × 10⁶ N/C
  5. 5. F = 91.04 N
  6. 6. F = 45.52 N

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