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
++2 µC−−6 µCr = ?

Point charges of +2 µC and −6 µC exert a force of 10 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 = 10 N
r = cm
2.Easy
−−4 µC++5 µCr = 2 cm

Two point charges of −4 µC and +5 µC are 2 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −4 µCq2 = +5 µCr = 2 cm
F = N
3.Medium
++5 µC−−3 µCP60 cm

A charge of +5 µC and a charge of −3 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 = +5 µCq2 = −3 µCr1 = 36 cmr2 = 24 cm
E = N/C
4.Medium
−−3 µC−−3 µC−−3 µC15 cm + 5 cm

Three point charges lie on a straight line: −3 µC on the left, −3 µC on the right 20 cm away, and −3 µC between them, 15 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 = −3 µCqR = −3 µCqM = −3 µCrL = 15 cmrR = 5 cm
F = N
5.Hard
+−P2 × 5 cm6 cm+3 µC−3 µC

Charges of +3 µC and −3 µC are 10 cm apart. Point P lies 6 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 = +3 µCq2 = −3 µCd = 10 cmh = 6 cm
E = N/C
6.Hard
L = 30 cm10°qq

Two identical small balls, each of mass 5 g, hang from the same point on insulating threads 30 cm long. They are given equal charges and each thread settles at 10° 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 = 5 gL = 30 cmθ = 10°g = 9.81 m/s²
q = nC

Answer key

  1. 1. r = 10.39 cm
  2. 2. F = 449.5 N
  3. 3. E = 815066 N/C
  4. 4. F = 28.77 N
  5. 5. E = 5.661 × 10⁶ N/C
  6. 6. q = 102.2 nC

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