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++10 µCr = 4 cm

Two point charges of −10 µC and +10 µC are 4 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −10 µCq2 = +10 µCr = 4 cm
F = N
2.Easy
−−5 µC−−8 µCr = 15 cm

Two point charges of −5 µC and −8 µC are 15 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −5 µCq2 = −8 µCr = 15 cm
F = N
3.Medium
++2 µC−−4 µCP40 cm

A charge of +2 µC and a charge of −4 µC are 40 cm apart. Point P lies on the line between them, 20 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +2 µCq2 = −4 µCr1 = 20 cmr2 = 20 cm
E = N/C
4.Medium
++1 µC−−1 µCP30 cm

A charge of +1 µC and a charge of −1 µC are 30 cm apart. Point P lies on the line between them, 22.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +1 µCq2 = −1 µCr1 = 22.5 cmr2 = 7.5 cm
E = N/C
5.Hard
+ + + + + +− − − − − −e⁻3 × 10⁷ m/s4 cmE = 3900 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 3 × 10⁷ m/s. The plates are 4 cm long and the field between them is 3900 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 × 10⁷ m/sL = 4 cmE = 3900 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
8 cm4 cm+q1​ = +5 µC+q3​ = +1 µC+q2​ = +4 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 1 µC is at the right-angle corner, q₁ = 5 µC is 8 cm from it along one side and q₂ = 4 µC is 4 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 5 µCq2 = 4 µCq3 = 1 µCr13 = 8 cmr23 = 4 cm
F = N

Answer key

  1. 1. F = 561.9 N
  2. 2. F = 15.98 N
  3. 3. E = 1.348 × 10⁶ N/C
  4. 4. E = 1.776 × 10⁶ N/C
  5. 5. y = 0.6097 mm
  6. 6. F = 23.55 N

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