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
++4 µC−−10 µCr = ?

Point charges of +4 µC and −10 µC exert a force of 1 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 = −10 µCF = 1 N
r = cm
2.Easy
++2 µC++6 µCr = ?

Point charges of +2 µC and +6 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 = +2 µCq2 = +6 µCF = 8 N
r = cm
3.Medium
++10 µC++1 µCE = 080 cm

Charges of +10 µC and +1 µC are 80 cm apart. At what distance x from the +10 µC charge, on the line between them, is the electric field zero?

q1 = +10 µCq2 = +1 µCd = 80 cm
x = cm
4.Medium
−−8 µC−−6 µC++4 µC16 cm + 24 cm

Three point charges lie on a straight line: −8 µC on the left, +4 µC on the right 40 cm away, and −6 µC between them, 16 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 = −8 µCqR = +4 µCqM = −6 µCrL = 16 cmrR = 24 cm
F = N
5.Hard
3 cm5 cm+q1​ = +2 µC+q3​ = +1 µC+q2​ = +4 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 1 µC is at the right-angle corner, q₁ = 2 µC is 3 cm from it along one side and q₂ = 4 µC is 5 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 2 µCq2 = 4 µCq3 = 1 µCr13 = 3 cmr23 = 5 cm
F = N
6.Hard
4 cm4 cm+q1​ = +4 µC+q3​ = +5 µC+q2​ = +6 µC

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

q1 = 4 µCq2 = 6 µCq3 = 5 µCr13 = 4 cmr23 = 4 cm
F = N

Answer key

  1. 1. r = 59.97 cm
  2. 2. r = 11.61 cm
  3. 3. x = 60.78 cm
  4. 4. F = 20.6 N
  5. 5. F = 24.62 N
  6. 6. F = 202.6 N

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