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
++40 nCPr = 3 cm

Find the magnitude of the electric field E at a distance of 3 cm from a point charge of +40 nC. Use k = 8.99 × 10⁹ N·m²/C².

q = +40 nCr = 3 cm
E = N/C
2.Easy
++8 µC++8 µCr = ?

Point charges of +8 µC and +8 µC exert a force of 8 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = +8 µCF = 8 N
r = cm
3.Medium
++8 µC++5 µCE = 020 cm

Charges of +8 µC and +5 µC are 20 cm apart. At what distance x from the +8 µC charge, on the line between them, is the electric field zero?

q1 = +8 µCq2 = +5 µCd = 20 cm
x = cm
4.Medium
++2 µC++6 µCE = 010 cm

Charges of +2 µC and +6 µC are 10 cm apart. At what distance x from the +2 µC charge, on the line between them, is the electric field zero?

q1 = +2 µCq2 = +6 µCd = 10 cm
x = cm
5.Hard
+ + + + + +− − − − − −e⁻4 × 10⁷ m/s6 cmE = 4900 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 4 × 10⁷ m/s. The plates are 6 cm long and the field between them is 4900 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 = 4 × 10⁷ m/sL = 6 cmE = 4900 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
4 cm6 cm+q1​ = +2 µC+q3​ = +2 µC+q2​ = +6 µC

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

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

Answer key

  1. 1. E = 399556 N/C
  2. 2. r = 26.82 cm
  3. 3. x = 11.17 cm
  4. 4. x = 3.66 cm
  5. 5. y = 0.9695 mm
  6. 6. F = 37.46 N

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