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
++6 µC++1 µCr = 30 cm

Two point charges of +6 µC and +1 µC are 30 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +6 µCq2 = +1 µCr = 30 cm
F = N
2.Easy
++8 µC−−8 µCr = ?

Point charges of +8 µC and −8 µC exert a force of 20 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 = 20 N
r = cm
3.Medium
−−6 µC−−6 µC++6 µC4 cm + 6 cm

Three point charges lie on a straight line: −6 µC on the left, +6 µC on the right 10 cm away, and −6 µC between them, 4 cm from the left charge. Find the magnitude of the net electric force F on the middle charge. Use k = 8.99 × 10⁹ N·m²/C².

qL = −6 µCqR = +6 µCqM = −6 µCrL = 4 cmrR = 6 cm
F = N
4.Medium
++6 µC++3 µCP40 cm

A charge of +6 µC and a charge of +3 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 = +6 µCq2 = +3 µCr1 = 30 cmr2 = 10 cm
E = N/C
5.Hard
L = 100 cm10°qq

Two identical small balls, each of mass 5 g, hang from the same point on insulating threads 100 cm long. They are given equal charges and each thread settles at 10° 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 = 100 cmθ = 10°g = 9.81 m/s²
q = nC
6.Hard
8 cm3 cm+q1​ = +8 µC+q3​ = +1 µC+q2​ = +4 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 1 µC is at the right-angle corner, q₁ = 8 µC is 8 cm from it along one side and q₂ = 4 µC is 3 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 8 µCq2 = 4 µCq3 = 1 µCr13 = 8 cmr23 = 3 cm
F = N

Answer key

  1. 1. F = 0.5993 N
  2. 2. r = 16.96 cm
  3. 3. F = 292.2 N
  4. 4. E = 2.098 × 10⁶ N/C
  5. 5. q = 340.6 nC
  6. 6. F = 41.51 N

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