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−−6 µCr = ?

Point charges of +8 µC and −6 µC exert a force of 2 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 = −6 µCF = 2 N
r = cm
2.Easy
++3 µC++5 µCr = ?

Point charges of +3 µC and +5 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 = +3 µCq2 = +5 µCF = 8 N
r = cm
3.Medium
++1 µC++5 µCE = 080 cm

Charges of +1 µC and +5 µC are 80 cm apart. At what distance x from the +1 µC charge, on the line between them, is the electric field zero?

q1 = +1 µCq2 = +5 µCd = 80 cm
x = cm
4.Medium
++3 µC++6 µCP60 cm

A charge of +3 µC and a charge of +6 µC are 60 cm apart. Point P lies on the line between them, 36 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +3 µCq2 = +6 µCr1 = 36 cmr2 = 24 cm
E = N/C
5.Hard
4 cm5 cm+q1​ = +1 µC+q3​ = +4 µC+q2​ = +6 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 4 µC is at the right-angle corner, q₁ = 1 µC is 4 cm from it along one side and q₂ = 6 µC is 5 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 1 µCq2 = 6 µCq3 = 4 µCr13 = 4 cmr23 = 5 cm
F = N
6.Hard
10 cm10 cm+q1​ = +8 µC+q3​ = +3 µC+q2​ = +8 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 10 cm from it along one side and q₂ = 8 µC is 10 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 8 µCq2 = 8 µCq3 = 3 µCr13 = 10 cmr23 = 10 cm
F = N

Answer key

  1. 1. r = 46.45 cm
  2. 2. r = 12.98 cm
  3. 3. x = 24.72 cm
  4. 4. E = 728356 N/C
  5. 5. F = 89.18 N
  6. 6. F = 30.51 N

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