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
++8 µC++10 µCr = 30 cm

Two point charges of +8 µC and +10 µC are 30 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = +10 µCr = 30 cm
F = N
2.Easy
++4 µCPr = 3 cm

Find the magnitude of the electric field E at a distance of 3 cm from a point charge of +4 µC. Use k = 8.99 × 10⁹ N·m²/C².

q = +4 µCr = 3 cm
E = N/C
3.Medium
++6 µC−−5 µCP10 cm

A charge of +6 µC and a charge of −5 µC are 10 cm apart. Point P lies on the line between them, 4 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +6 µCq2 = −5 µCr1 = 4 cmr2 = 6 cm
E = N/C
4.Medium
++8 µC++3 µCP20 cm

A charge of +8 µC and a charge of +3 µC are 20 cm apart. Point P lies on the line between them, 10 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +8 µCq2 = +3 µCr1 = 10 cmr2 = 10 cm
E = N/C
5.Hard
L = 80 cm12°qq

Two identical small balls, each of mass 8 g, hang from the same point on insulating threads 80 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 = 8 gL = 80 cmθ = 12°g = 9.81 m/s²
q = nC
6.Hard
+ + + + + +− − − − − −e⁻4.5 × 10⁷ m/s10 cmE = 1000 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 4.5 × 10⁷ m/s. The plates are 10 cm long and the field between them is 1000 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 = 4.5 × 10⁷ m/sL = 10 cmE = 1000 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. F = 7.991 N
  2. 2. E = 3.996 × 10⁷ N/C
  3. 3. E = 4.62 × 10⁷ N/C
  4. 4. E = 4.495 × 10⁶ N/C
  5. 5. q = 453.1 nC
  6. 6. y = 0.4342 mm

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