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−−5 µCr = ?

Point charges of +4 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 = +4 µCq2 = −5 µCF = 5 N
r = cm
2.Easy
++2 µCPr = 40 cm

Find the magnitude of the electric field E at a distance of 40 cm from a point charge of +2 µC. Use k = 8.99 × 10⁹ N·m²/C².

q = +2 µCr = 40 cm
E = N/C
3.Medium
++3 µC++2 µCP40 cm

A charge of +3 µC and a charge of +2 µC are 40 cm apart. Point P lies on the line between them, 30 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +3 µCq2 = +2 µCr1 = 30 cmr2 = 10 cm
E = N/C
4.Medium
++4 µC++2 µCP30 cm

A charge of +4 µC and a charge of +2 µC are 30 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 = +2 µCr1 = 15 cmr2 = 15 cm
E = N/C
5.Hard
10 cm4 cm+q1​ = +3 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 = 3 µC is 10 cm from it along one side and q₂ = 6 µC is 4 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 3 µCq2 = 6 µCq3 = 3 µCr13 = 10 cmr23 = 4 cm
F = N
6.Hard
6 cm5 cm+q1​ = +3 µC+q3​ = +10 µC+q2​ = +1 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 10 µC is at the right-angle corner, q₁ = 3 µC is 6 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 = 3 µCq2 = 1 µCq3 = 10 µCr13 = 6 cmr23 = 5 cm
F = N

Answer key

  1. 1. r = 18.96 cm
  2. 2. E = 112375 N/C
  3. 3. E = 1.498 × 10⁶ N/C
  4. 4. E = 799111 N/C
  5. 5. F = 101.5 N
  6. 6. F = 83.1 N

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