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
−−10 µC++5 µCr = 6 cm

Two point charges of −10 µC and +5 µC are 6 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −10 µCq2 = +5 µCr = 6 cm
F = N
2.Easy
+ + + + + +− − − − − −e⁻E = 2400 N/C

A proton (charge 1.602 × 10⁻¹⁹ C, mass 1.673 × 10⁻²⁷ kg) is in a uniform electric field of 2400 N/C. Ignoring gravity, find the magnitude of its acceleration a.

E = 2400 N/C|q| = 1.602 × 10⁻¹⁹ Cm = 1.673 × 10⁻²⁷ kg
a = m/s²
3.Medium
++2 µC−−8 µCP60 cm

A charge of +2 µC and a charge of −8 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 = +2 µCq2 = −8 µCr1 = 36 cmr2 = 24 cm
E = N/C
4.Medium
++8 µC++8 µCP20 cm

A charge of +8 µC and a charge of +8 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 = +8 µCq2 = +8 µCr1 = 12 cmr2 = 8 cm
E = N/C
5.Hard
+ + + + + +− − − − − −e⁻3.5 × 10⁷ m/s10 cmE = 3800 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 3.5 × 10⁷ m/s. The plates are 10 cm long and the field between them is 3800 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 = 3.5 × 10⁷ m/sL = 10 cmE = 3800 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
L = 20 cm15°qq

Two identical small balls, each of mass 10 g, hang from the same point on insulating threads 20 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 = 10 gL = 20 cmθ = 15°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 124.9 N
  2. 2. a = 2.298 × 10¹¹ m/s²
  3. 3. E = 1.387 × 10⁶ N/C
  4. 4. E = 6.243 × 10⁶ N/C
  5. 5. y = 2.728 mm
  6. 6. q = 177 nC

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