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++1 µCr = 15 cm

Two point charges of −3 µC and +1 µC are 15 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −3 µCq2 = +1 µCr = 15 cm
F = N
2.Easy
−−5 µC++2 µCr = 4 cm

Two point charges of −5 µC and +2 µC are 4 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −5 µCq2 = +2 µCr = 4 cm
F = N
3.Medium
++5 µC−−6 µCP20 cm

A charge of +5 µC and a charge of −6 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 = +5 µCq2 = −6 µCr1 = 15 cmr2 = 5 cm
E = N/C
4.Medium
++3 µC−−1 µCP10 cm

A charge of +3 µC and a charge of −1 µC are 10 cm apart. Point P lies on the line between them, 2.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +3 µCq2 = −1 µCr1 = 2.5 cmr2 = 7.5 cm
E = N/C
5.Hard
L = 50 cm12°qq

Two identical small balls, each of mass 10 g, hang from the same point on insulating threads 50 cm long. They are given equal charges and each thread settles at 12° 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 = 10 gL = 50 cmθ = 12°g = 9.81 m/s²
q = nC
6.Hard
4 cm6 cm+q1​ = +6 µC+q3​ = +1 µC+q2​ = +8 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 1 µC is at the right-angle corner, q₁ = 6 µC is 4 cm from it along one side and q₂ = 8 µC is 6 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 6 µCq2 = 8 µCq3 = 1 µCr13 = 4 cmr23 = 6 cm
F = N

Answer key

  1. 1. F = 1.199 N
  2. 2. F = 56.19 N
  3. 3. E = 2.357 × 10⁷ N/C
  4. 4. E = 4.475 × 10⁷ N/C
  5. 5. q = 316.6 nC
  6. 6. F = 39.19 N

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