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
+q₁+q₂r

Two point charges repel each other with a force of 16 N. The first charge is made four times as large and the distance between the charges is tripled. Find the new force F′.

F = 16 Nq₁′ = 4·q₁r′ = 3·r
F′ = N
2.Easy
−−2 µC++1 µCr = 3 cm

Two point charges of −2 µC and +1 µC are 3 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −2 µCq2 = +1 µCr = 3 cm
F = N
3.Medium
++2 µC++6 µCP30 cm

A charge of +2 µC and a charge of +6 µC are 30 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 = +2 µCq2 = +6 µCr1 = 15 cmr2 = 15 cm
E = N/C
4.Medium
++1 µC++4 µC++3 µC22.5 cm + 7.5 cm

Three point charges lie on a straight line: +1 µC on the left, +3 µC on the right 30 cm away, and +4 µC between them, 22.5 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 = +1 µCqR = +3 µCqM = +4 µCrL = 22.5 cmrR = 7.5 cm
F = N
5.Hard
4 cm8 cm+q1​ = +10 µC+q3​ = +8 µC+q2​ = +10 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 8 µC is at the right-angle corner, q₁ = 10 µC is 4 cm from it along one side and q₂ = 10 µC is 8 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 10 µCq2 = 10 µCq3 = 8 µCr13 = 4 cmr23 = 8 cm
F = N
6.Hard
5 cm3 cm+q1​ = +10 µC+q3​ = +10 µC+q2​ = +5 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 10 µC is at the right-angle corner, q₁ = 10 µC is 5 cm from it along one side and q₂ = 5 µC is 3 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 10 µCq2 = 5 µCq3 = 10 µCr13 = 5 cmr23 = 3 cm
F = N

Answer key

  1. 1. F′ = 7.111 N
  2. 2. F = 19.98 N
  3. 3. E = 1.598 × 10⁶ N/C
  4. 4. F = 18.47 N
  5. 5. F = 463.3 N
  6. 6. F = 615.4 N

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