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
++4 µC−−8 µCr = 30 cm

Two point charges of +4 µC and −8 µC are 30 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +4 µCq2 = −8 µCr = 30 cm
F = N
2.Easy
−−1 µCPr = 20 cm

Find the magnitude of the electric field E at a distance of 20 cm from a point charge of −1 µC. Use k = 8.99 × 10⁹ N·m²/C².

q = −1 µCr = 20 cm
E = N/C
3.Medium
−−2 µC++10 µCr = 40 cm

Two identical small metal spheres carry charges of −2 µC and +10 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 = −2 µCq2 = +10 µCr = 40 cm
F = N
4.Medium
++6 µC−−3 µCP50 cm

A charge of +6 µC and a charge of −3 µC are 50 cm apart. Point P lies on the line between them, 12.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +6 µCq2 = −3 µCr1 = 12.5 cmr2 = 37.5 cm
E = N/C
5.Hard
10 cm10 cm+q1​ = +1 µC+q3​ = +10 µC+q2​ = +1 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 10 µC is at the right-angle corner, q₁ = 1 µC is 10 cm from it along one side and q₂ = 1 µC is 10 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 1 µCq2 = 1 µCq3 = 10 µCr13 = 10 cmr23 = 10 cm
F = N
6.Hard
+ + + + + +− − − − − −e⁻1 × 10⁷ m/s3 cmE = 700 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 1 × 10⁷ m/s. The plates are 3 cm long and the field between them is 700 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 = 3 cmE = 700 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. F = 3.196 N
  2. 2. E = 224750 N/C
  3. 3. F = 0.899 N
  4. 4. E = 3.644 × 10⁶ N/C
  5. 5. F = 12.71 N
  6. 6. y = 0.554 mm

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