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−−10 µCr = ?

Point charges of +3 µC and −10 µC exert a force of 50 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = −10 µCF = 50 N
r = cm
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 46 N. The first charge is made four times as large and the distance between the charges is halved. Find the new force F′.

F = 46 Nq₁′ = 4·q₁r′ = 0.5·r
F′ = N
3.Medium
++4 µC++3 µCP30 cm

A charge of +4 µC and a charge of +3 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 = +4 µCq2 = +3 µCr1 = 15 cmr2 = 15 cm
E = N/C
4.Medium
++8 µC−−1 µCr = 20 cm

Two identical small metal spheres carry charges of +8 µC and −1 µC. They are touched together and then put back 20 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = −1 µCr = 20 cm
F = N
5.Hard
3 cm4 cm+q1​ = +10 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 = 10 µC is 3 cm from it along one side and q₂ = 3 µC is 4 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 10 µCq2 = 3 µCq3 = 10 µCr13 = 3 cmr23 = 4 cm
F = N
6.Hard
6 cm5 cm+q1​ = +2 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 = 2 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 = 2 µCq2 = 3 µCq3 = 6 µCr13 = 6 cmr23 = 5 cm
F = N

Answer key

  1. 1. r = 7.344 cm
  2. 2. F′ = 736 N
  3. 3. E = 399556 N/C
  4. 4. F = 2.753 N
  5. 5. F = 1013 N
  6. 6. F = 71.33 N

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