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
−−10 µCPr = 20 cm

Find the magnitude of the electric field E at a distance of 20 cm from a point charge of −10 µC. Use k = 8.99 × 10⁹ N·m²/C².

q = −10 µCr = 20 cm
E = N/C
2.Easy
++4 µC++4 µCr = ?

Point charges of +4 µC and +4 µC exert a force of 5 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +4 µCq2 = +4 µCF = 5 N
r = cm
3.Medium
++2 µC++8 µCE = 050 cm

Charges of +2 µC and +8 µC are 50 cm apart. At what distance x from the +2 µC charge, on the line between them, is the electric field zero?

q1 = +2 µCq2 = +8 µCd = 50 cm
x = cm
4.Medium
++6 µC++10 µCr = 20 cm

Two identical small metal spheres carry charges of +6 µC and +10 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 = +6 µCq2 = +10 µCr = 20 cm
F = N
5.Hard
10 cm3 cm+q1​ = +5 µC+q3​ = +10 µC+q2​ = +8 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 10 µC is at the right-angle corner, q₁ = 5 µC is 10 cm from it along one side and q₂ = 8 µC is 3 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

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

Answer key

  1. 1. E = 2.247 × 10⁶ N/C
  2. 2. r = 16.96 cm
  3. 3. x = 16.67 cm
  4. 4. F = 14.38 N
  5. 5. F = 800.4 N
  6. 6. F = 46.73 N

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