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
−−50 nCPr = 10 cm

Find the magnitude of the electric field E at a distance of 10 cm from a point charge of −50 nC. Use k = 8.99 × 10⁹ N·m²/C².

q = −50 nCr = 10 cm
E = N/C
2.Easy
−−1 µC++1 µCr = 2 cm

Two point charges of −1 µC and +1 µC are 2 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −1 µCq2 = +1 µCr = 2 cm
F = N
3.Medium
−−4 µC−−3 µCr = 40 cm

Two identical small metal spheres carry charges of −4 µC and −3 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 = −4 µCq2 = −3 µCr = 40 cm
F = N
4.Medium
++3 µC++8 µCr = 20 cm

Two identical small metal spheres carry charges of +3 µC and +8 µC. They are touched together and then put back 20 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = +8 µCr = 20 cm
F = N
5.Hard
3 cm10 cm+q1​ = +4 µC+q3​ = +10 µC+q2​ = +3 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 10 µC is at the right-angle corner, q₁ = 4 µC is 3 cm from it along one side and q₂ = 3 µC is 10 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 4 µCq2 = 3 µCq3 = 10 µCr13 = 3 cmr23 = 10 cm
F = N
6.Hard
+ + + + + +− − − − − −e⁻3.5 × 10⁷ m/s10 cmE = 500 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 500 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 = 500 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. E = 44950 N/C
  2. 2. F = 22.47 N
  3. 3. F = 0.6883 N
  4. 4. F = 6.799 N
  5. 5. F = 400.5 N
  6. 6. y = 0.3589 mm

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