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
++3 µC−−2 µCr = 5 cm

Two point charges of +3 µC and −2 µC are 5 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = −2 µCr = 5 cm
F = N
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 46 N. The first charge is doubled and the distance between the charges is tripled. Find the new force F′.

F = 46 Nq₁′ = 2·q₁r′ = 3·r
F′ = N
3.Medium
++2 µC−−1 µCP20 cm

A charge of +2 µC and a charge of −1 µC are 20 cm apart. Point P lies on the line between them, 12 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +2 µCq2 = −1 µCr1 = 12 cmr2 = 8 cm
E = N/C
4.Medium
++5 µC++8 µC−−3 µC12 cm + 8 cm

Three point charges lie on a straight line: +5 µC on the left, −3 µC on the right 20 cm away, and +8 µC between them, 12 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 = +8 µCrL = 12 cmrR = 8 cm
F = N
5.Hard
L = 100 cm12°qq

Two identical small balls, each of mass 1 g, hang from the same point on insulating threads 100 cm long. They are given equal charges and each thread settles at 12° 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 = 1 gL = 100 cmθ = 12°g = 9.81 m/s²
q = nC
6.Hard
+ + + + + +− − − − − −e⁻1.5 × 10⁷ m/s4 cmE = 1100 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 1.5 × 10⁷ m/s. The plates are 4 cm long and the field between them is 1100 N/C. Electron charge 1.602 × 10⁻¹⁹ C, mass 9.109 × 10⁻³¹ kg; ignore gravity. How far y is it deflected sideways when it leaves the plates? Give the answer in mm.

v₀ = 1.5 × 10⁷ m/sL = 4 cmE = 1100 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. F = 21.58 N
  2. 2. F′ = 10.22 N
  3. 3. E = 2.653 × 10⁶ N/C
  4. 4. F = 58.68 N
  5. 5. q = 200.3 nC
  6. 6. y = 0.6878 mm

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