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
−−3 µCPr = 2 cm

Find the magnitude of the electric field E at a distance of 2 cm from a point charge of −3 µC. Use k = 8.99 × 10⁹ N·m²/C².

q = −3 µCr = 2 cm
E = N/C
2.Easy
−−2 µC−−5 µCr = 10 cm

Two point charges of −2 µC and −5 µC are 10 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −2 µCq2 = −5 µCr = 10 cm
F = N
3.Medium
−−1 µC−−5 µCr = 20 cm

Two identical small metal spheres carry charges of −1 µC and −5 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 = −1 µCq2 = −5 µCr = 20 cm
F = N
4.Medium
++1 µC−−8 µC−−2 µC7.5 cm + 22.5 cm

Three point charges lie on a straight line: +1 µC on the left, −2 µC on the right 30 cm away, and −8 µC between them, 7.5 cm from the left charge. Find the magnitude of the net electric force F on the middle charge. Use k = 8.99 × 10⁹ N·m²/C².

qL = +1 µCqR = −2 µCqM = −8 µCrL = 7.5 cmrR = 22.5 cm
F = N
5.Hard
+ + + + + +− − − − − −e⁻2 × 10⁷ m/s8 cmE = 1500 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 2 × 10⁷ m/s. The plates are 8 cm long and the field between them is 1500 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 = 2 × 10⁷ m/sL = 8 cmE = 1500 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
4 cm5 cm+q1​ = +1 µC+q3​ = +3 µC+q2​ = +6 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 3 µC is at the right-angle corner, q₁ = 1 µC is 4 cm from it along one side and q₂ = 6 µC is 5 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 1 µCq2 = 6 µCq3 = 3 µCr13 = 4 cmr23 = 5 cm
F = N

Answer key

  1. 1. E = 6.742 × 10⁷ N/C
  2. 2. F = 8.99 N
  3. 3. F = 2.023 N
  4. 4. F = 15.63 N
  5. 5. y = 2.11 mm
  6. 6. F = 66.89 N

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