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++6 µCr = 4 cm

Two point charges of +3 µC and +6 µC are 4 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = +6 µCr = 4 cm
F = N
2.Easy
++5 µC−−8 µCr = 3 cm

Two point charges of +5 µC and −8 µC are 3 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +5 µCq2 = −8 µCr = 3 cm
F = N
3.Medium
++10 µC++1 µCr = 25 cm

Two identical small metal spheres carry charges of +10 µC and +1 µC. They are touched together and then put back 25 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +10 µCq2 = +1 µCr = 25 cm
F = N
4.Medium
++2 µC++10 µCE = 030 cm

Charges of +2 µC and +10 µC are 30 cm apart. At what distance x from the +2 µC charge, on the line between them, is the electric field zero?

q1 = +2 µCq2 = +10 µCd = 30 cm
x = cm
5.Hard
3 cm6 cm+q1​ = +10 µC+q3​ = +1 µC+q2​ = +6 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 1 µC is at the right-angle corner, q₁ = 10 µC is 3 cm from it along one side and q₂ = 6 µC is 6 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 10 µCq2 = 6 µCq3 = 1 µCr13 = 3 cmr23 = 6 cm
F = N
6.Hard
L = 20 cm10°qq

Two identical small balls, each of mass 5 g, hang from the same point on insulating threads 20 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 = 20 cmθ = 10°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 101.1 N
  2. 2. F = 399.6 N
  3. 3. F = 4.351 N
  4. 4. x = 9.271 cm
  5. 5. F = 101 N
  6. 6. q = 68.13 nC

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