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
−−5 µC++10 µCr = 2 cm

Two point charges of −5 µC and +10 µC are 2 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −5 µCq2 = +10 µCr = 2 cm
F = N
2.Easy
++1 µC++3 µCr = 15 cm

Two point charges of +1 µC and +3 µC are 15 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +1 µCq2 = +3 µCr = 15 cm
F = N
3.Medium
++2 µC++10 µCE = 060 cm

Charges of +2 µC and +10 µC are 60 cm apart. At what distance x from the +2 µC charge, on the line between them, is the electric field zero?

q1 = +2 µCq2 = +10 µCd = 60 cm
x = cm
4.Medium
++5 µC−−3 µC++3 µC30 cm + 10 cm

Three point charges lie on a straight line: +5 µC on the left, +3 µC on the right 40 cm away, and −3 µC between them, 30 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 = +5 µCqR = +3 µCqM = −3 µCrL = 30 cmrR = 10 cm
F = N
5.Hard
L = 40 cm5°qq

Two identical small balls, each of mass 10 g, hang from the same point on insulating threads 40 cm long. They are given equal charges and each thread settles at 5° from the vertical. Use g = 9.81 m/s². Find the charge q on each ball in nC. Use k = 8.99 × 10⁹ N·m²/C².

m = 10 gL = 40 cmθ = 5°g = 9.81 m/s²
q = nC
6.Hard
8 cm3 cm+q1​ = +6 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 = 6 µC is 8 cm from it along one side and q₂ = 3 µC is 3 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 6 µCq2 = 3 µCq3 = 6 µCr13 = 8 cmr23 = 3 cm
F = N

Answer key

  1. 1. F = 1124 N
  2. 2. F = 1.199 N
  3. 3. x = 18.54 cm
  4. 4. F = 6.593 N
  5. 5. q = 68.13 nC
  6. 6. F = 186.8 N

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