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++1 µCr = ?

Point charges of +2 µC and +1 µC exert a force of 20 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 = +1 µCF = 20 N
r = cm
2.Easy
−−6 µC−−10 µCr = 2 cm

Two point charges of −6 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 = −6 µCq2 = −10 µCr = 2 cm
F = N
3.Medium
++3 µC−−3 µCP40 cm

A charge of +3 µC and a charge of −3 µC are 40 cm apart. Point P lies on the line between them, 30 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +3 µCq2 = −3 µCr1 = 30 cmr2 = 10 cm
E = N/C
4.Medium
++3 µC++3 µCP40 cm

A charge of +3 µC and a charge of +3 µC are 40 cm apart. Point P lies on the line between them, 30 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +3 µCq2 = +3 µCr1 = 30 cmr2 = 10 cm
E = N/C
5.Hard
L = 40 cm15°qq

Two identical small balls, each of mass 2 g, hang from the same point on insulating threads 40 cm long. They are given equal charges and each thread settles at 15° 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 = 2 gL = 40 cmθ = 15°g = 9.81 m/s²
q = nC
6.Hard
++P2 × 5 cm5 cm+4 µC+4 µC

Charges of +4 µC and +4 µC are 10 cm apart. Point P lies 5 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 = +4 µCq2 = +4 µCd = 10 cmh = 5 cm
E = N/C

Answer key

  1. 1. r = 2.998 cm
  2. 2. F = 1349 N
  3. 3. E = 2.997 × 10⁶ N/C
  4. 4. E = 2.397 × 10⁶ N/C
  5. 5. q = 158.3 nC
  6. 6. E = 1.017 × 10⁷ N/C

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