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
++6 µCPr = 20 cm

Find the magnitude of the electric field E at a distance of 20 cm from a point charge of +6 µC. Use k = 8.99 × 10⁹ N·m²/C².

q = +6 µCr = 20 cm
E = N/C
2.Easy
+ + + + + +− − − − − −e⁻E = 4800 N/C

A proton (charge 1.602 × 10⁻¹⁹ C, mass 1.673 × 10⁻²⁷ kg) is in a uniform electric field of 4800 N/C. Ignoring gravity, find the magnitude of its acceleration a.

E = 4800 N/C|q| = 1.602 × 10⁻¹⁹ Cm = 1.673 × 10⁻²⁷ kg
a = m/s²
3.Medium
++10 µC++4 µCP30 cm

A charge of +10 µC and a charge of +4 µC are 30 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 = +10 µCq2 = +4 µCr1 = 12 cmr2 = 18 cm
E = N/C
4.Medium
++3 µC++8 µCP30 cm

A charge of +3 µC and a charge of +8 µC are 30 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 = +3 µCq2 = +8 µCr1 = 12 cmr2 = 18 cm
E = N/C
5.Hard
6 cm10 cm+q1​ = +6 µC+q3​ = +10 µC+q2​ = +6 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 10 µC is at the right-angle corner, q₁ = 6 µC is 6 cm from it along one side and q₂ = 6 µC is 10 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 6 µCq2 = 6 µCq3 = 10 µCr13 = 6 cmr23 = 10 cm
F = N
6.Hard
+ + + + + +− − − − − −e⁻1 × 10⁷ m/s4 cmE = 4300 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 1 × 10⁷ m/s. The plates are 4 cm long and the field between them is 4300 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 × 10⁷ m/sL = 4 cmE = 4300 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. E = 1.348 × 10⁶ N/C
  2. 2. a = 4.596 × 10¹¹ m/s²
  3. 3. E = 5.133 × 10⁶ N/C
  4. 4. E = 346836 N/C
  5. 5. F = 159.2 N
  6. 6. y = 6.05 mm

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