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++4 µCr = 30 cm

Two point charges of +10 µC and +4 µC are 30 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +10 µCq2 = +4 µCr = 30 cm
F = N
2.Easy
−−3 µC++3 µCr = 15 cm

Two point charges of −3 µC and +3 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 = +3 µCr = 15 cm
F = N
3.Medium
++1 µC++3 µCP10 cm

A charge of +1 µC and a charge of +3 µC are 10 cm apart. Point P lies on the line between them, 6 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +1 µCq2 = +3 µCr1 = 6 cmr2 = 4 cm
E = N/C
4.Medium
++8 µC−−3 µCP60 cm

A charge of +8 µC and a charge of −3 µC are 60 cm apart. Point P lies on the line between them, 45 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +8 µCq2 = −3 µCr1 = 45 cmr2 = 15 cm
E = N/C
5.Hard
L = 60 cm15°qq

Two identical small balls, each of mass 10 g, hang from the same point on insulating threads 60 cm long. They are given equal charges and each thread settles at 15° 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 = 60 cmθ = 15°g = 9.81 m/s²
q = nC
6.Hard
8 cm5 cm+q1​ = +8 µC+q3​ = +3 µC+q2​ = +5 µC

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

q1 = 8 µCq2 = 5 µCq3 = 3 µCr13 = 8 cmr23 = 5 cm
F = N

Answer key

  1. 1. F = 3.996 N
  2. 2. F = 3.596 N
  3. 3. E = 1.436 × 10⁷ N/C
  4. 4. E = 1.554 × 10⁶ N/C
  5. 5. q = 531.1 nC
  6. 6. F = 63.61 N

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