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 µCPr = 25 cm

Find the magnitude of the electric field E at a distance of 25 cm from a point charge of −6 µC. Use k = 8.99 × 10⁹ N·m²/C².

q = −6 µCr = 25 cm
E = N/C
2.Easy
−−4 µC++10 µCr = 3 cm

Two point charges of −4 µC and +10 µC are 3 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −4 µCq2 = +10 µCr = 3 cm
F = N
3.Medium
++2 µC++5 µCr = 40 cm

Two identical small metal spheres carry charges of +2 µC and +5 µC. They are touched together and then put back 40 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +2 µCq2 = +5 µCr = 40 cm
F = N
4.Medium
−−1 µC++10 µCr = 40 cm

Two identical small metal spheres carry charges of −1 µC and +10 µC. They are touched together and then put back 40 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −1 µCq2 = +10 µCr = 40 cm
F = N
5.Hard
6 cm5 cm+q1​ = +8 µC+q3​ = +6 µC+q2​ = +3 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 6 µC is at the right-angle corner, q₁ = 8 µC is 6 cm from it along one side and q₂ = 3 µC is 5 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 8 µCq2 = 3 µCq3 = 6 µCr13 = 6 cmr23 = 5 cm
F = N
6.Hard
L = 30 cm5°qq

Two identical small balls, each of mass 1 g, hang from the same point on insulating threads 30 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 = 1 gL = 30 cmθ = 5°g = 9.81 m/s²
q = nC

Answer key

  1. 1. E = 863040 N/C
  2. 2. F = 399.6 N
  3. 3. F = 0.6883 N
  4. 4. F = 1.138 N
  5. 5. F = 136.2 N
  6. 6. q = 16.16 nC

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