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
++10 µC−−3 µCr = 2 cm

Two point charges of +10 µC and −3 µC are 2 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +10 µCq2 = −3 µCr = 2 cm
F = N
2.Easy
++1 µC++3 µCr = ?

Point charges of +1 µC and +3 µC exert a force of 10 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 = +3 µCF = 10 N
r = cm
3.Medium
++5 µC−−2 µCP60 cm

A charge of +5 µC and a charge of −2 µC are 60 cm apart. Point P lies on the line between them, 36 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +5 µCq2 = −2 µCr1 = 36 cmr2 = 24 cm
E = N/C
4.Medium
++3 µC++8 µCP30 cm

A charge of +3 µC and a charge of +8 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 = +3 µCq2 = +8 µCr1 = 15 cmr2 = 15 cm
E = N/C
5.Hard
6 cm5 cm+q1​ = +3 µC+q3​ = +8 µC+q2​ = +1 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 8 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 = 8 µCr13 = 6 cmr23 = 5 cm
F = N
6.Hard
L = 60 cm5°qq

Two identical small balls, each of mass 5 g, hang from the same point on insulating threads 60 cm long. They are given equal charges and each thread settles at 5° from the vertical. Use g = 9.81 m/s². Find the charge q on each ball in nC. Use k = 8.99 × 10⁹ N·m²/C².

m = 5 gL = 60 cmθ = 5°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 674.3 N
  2. 2. r = 5.193 cm
  3. 3. E = 658989 N/C
  4. 4. E = 1.998 × 10⁶ N/C
  5. 5. F = 66.48 N
  6. 6. q = 72.26 nC

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