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 µC++8 µCr = 2 cm

Two point charges of +6 µC and +8 µC are 2 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +6 µCq2 = +8 µCr = 2 cm
F = N
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 12 N. The first charge is tripled and the distance between the charges is made four times as large. Find the new force F′.

F = 12 Nq₁′ = 3·q₁r′ = 4·r
F′ = N
3.Medium
++10 µC−−10 µC−−5 µC20 cm + 20 cm

Three point charges lie on a straight line: +10 µC on the left, −5 µC on the right 40 cm away, and −10 µC between them, 20 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 = +10 µCqR = −5 µCqM = −10 µCrL = 20 cmrR = 20 cm
F = N
4.Medium
++1 µC++3 µCP50 cm

A charge of +1 µC and a charge of +3 µC are 50 cm apart. Point P lies on the line between them, 12.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +1 µCq2 = +3 µCr1 = 12.5 cmr2 = 37.5 cm
E = N/C
5.Hard
8 cm5 cm+q1​ = +3 µC+q3​ = +8 µC+q2​ = +1 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 8 µC is at the right-angle corner, q₁ = 3 µC is 8 cm from it along one side and q₂ = 1 µC is 5 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 3 µCq2 = 1 µCq3 = 8 µCr13 = 8 cmr23 = 5 cm
F = N
6.Hard
10 cm5 cm+q1​ = +4 µC+q3​ = +10 µC+q2​ = +3 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 10 µC is at the right-angle corner, q₁ = 4 µC is 10 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 = 4 µCq2 = 3 µCq3 = 10 µCr13 = 10 cmr23 = 5 cm
F = N

Answer key

  1. 1. F = 1079 N
  2. 2. F′ = 2.25 N
  3. 3. F = 33.71 N
  4. 4. E = 383573 N/C
  5. 5. F = 44.32 N
  6. 6. F = 113.7 N

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