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 µCPr = 15 cm

Find the magnitude of the electric field E at a distance of 15 cm from a point charge of +4 µC. Use k = 8.99 × 10⁹ N·m²/C².

q = +4 µCr = 15 cm
E = N/C
2.Easy
−−1 µC−−4 µCr = 3 cm

Two point charges of −1 µC and −4 µC are 3 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −1 µCq2 = −4 µCr = 3 cm
F = N
3.Medium
++1 µC−−2 µCP30 cm

A charge of +1 µC and a charge of −2 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 = +1 µCq2 = −2 µCr1 = 12 cmr2 = 18 cm
E = N/C
4.Medium
++5 µC++3 µCE = 080 cm

Charges of +5 µC and +3 µC are 80 cm apart. At what distance x from the +5 µC charge, on the line between them, is the electric field zero?

q1 = +5 µCq2 = +3 µCd = 80 cm
x = cm
5.Hard
+ + + + + +− − − − − −e⁻3.5 × 10⁷ m/s5 cmE = 4000 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 5 cm long and the field between them is 4000 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 = 5 cmE = 4000 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
6 cm4 cm+q1​ = +10 µC+q3​ = +5 µC+q2​ = +2 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 5 µC is at the right-angle corner, q₁ = 10 µC is 6 cm from it along one side and q₂ = 2 µC is 4 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 10 µCq2 = 2 µCq3 = 5 µCr13 = 6 cmr23 = 4 cm
F = N

Answer key

  1. 1. E = 1.598 × 10⁶ N/C
  2. 2. F = 39.96 N
  3. 3. E = 1.179 × 10⁶ N/C
  4. 4. x = 45.08 cm
  5. 5. y = 0.7178 mm
  6. 6. F = 136.9 N

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