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
++8 µC++3 µCr = ?

Point charges of +8 µC and +3 µC exert a force of 8 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = +3 µCF = 8 N
r = cm
2.Easy
++3 µC++8 µCr = ?

Point charges of +3 µC and +8 µC exert a force of 20 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 = +8 µCF = 20 N
r = cm
3.Medium
++6 µC−−3 µCP60 cm

A charge of +6 µC and a charge of −3 µC are 60 cm apart. Point P lies on the line between them, 24 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +6 µCq2 = −3 µCr1 = 24 cmr2 = 36 cm
E = N/C
4.Medium
++10 µC++4 µCr = 30 cm

Two identical small metal spheres carry charges of +10 µC and +4 µC. They are touched together and then put back 30 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +10 µCq2 = +4 µCr = 30 cm
F = N
5.Hard
+−P2 × 3 cm4 cm+4 µC−4 µC

Charges of +4 µC and −4 µC are 6 cm apart. Point P lies 4 cm from the midpoint between them, on the perpendicular bisector. Find the magnitude of the electric field E at P. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +4 µCq2 = −4 µCd = 6 cmh = 4 cm
E = N/C
6.Hard
4 cm8 cm+q1​ = +2 µC+q3​ = +4 µC+q2​ = +10 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 4 µC is at the right-angle corner, q₁ = 2 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 = 2 µCq2 = 10 µCq3 = 4 µCr13 = 4 cmr23 = 8 cm
F = N

Answer key

  1. 1. r = 16.42 cm
  2. 2. r = 10.39 cm
  3. 3. E = 1.145 × 10⁶ N/C
  4. 4. F = 4.895 N
  5. 5. E = 1.726 × 10⁷ N/C
  6. 6. F = 71.96 N

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