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−−3 µCr = 25 cm

Two point charges of +2 µC and −3 µC are 25 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +2 µCq2 = −3 µCr = 25 cm
F = N
2.Easy
+ + + + + +− − − − − −e⁻E = 1300 N/C

A proton (charge 1.602 × 10⁻¹⁹ C, mass 1.673 × 10⁻²⁷ kg) is in a uniform electric field of 1300 N/C. Ignoring gravity, find the magnitude of its acceleration a.

E = 1300 N/C|q| = 1.602 × 10⁻¹⁹ Cm = 1.673 × 10⁻²⁷ kg
a = m/s²
3.Medium
++4 µC++5 µCP40 cm

A charge of +4 µC and a charge of +5 µC are 40 cm apart. Point P lies on the line between them, 20 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +4 µCq2 = +5 µCr1 = 20 cmr2 = 20 cm
E = N/C
4.Medium
−−5 µC−−3 µCr = 40 cm

Two identical small metal spheres carry charges of −5 µC and −3 µC. They are touched together and then put back 40 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −5 µCq2 = −3 µCr = 40 cm
F = N
5.Hard
L = 80 cm15°qq

Two identical small balls, each of mass 2 g, hang from the same point on insulating threads 80 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 = 80 cmθ = 15°g = 9.81 m/s²
q = nC
6.Hard
+−P2 × 3 cm6 cm+3 µC−3 µC

Charges of +3 µC and −3 µC are 6 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 = 6 cmh = 6 cm
E = N/C

Answer key

  1. 1. F = 0.863 N
  2. 2. a = 1.245 × 10¹¹ m/s²
  3. 3. E = 224750 N/C
  4. 4. F = 0.899 N
  5. 5. q = 316.7 nC
  6. 6. E = 5.361 × 10⁶ N/C

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