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 = 30 cm

Find the magnitude of the electric field E at a distance of 30 cm from a point charge of −40 nC. Use k = 8.99 × 10⁹ N·m²/C².

q = −40 nCr = 30 cm
E = N/C
2.Easy
++8 µC−−5 µCr = ?

Point charges of +8 µC and −5 µC exert a force of 0.5 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 = −5 µCF = 0.5 N
r = cm
3.Medium
++1 µC++6 µCE = 050 cm

Charges of +1 µC and +6 µC are 50 cm apart. At what distance x from the +1 µC charge, on the line between them, is the electric field zero?

q1 = +1 µCq2 = +6 µCd = 50 cm
x = cm
4.Medium
++10 µC++10 µCP60 cm

A charge of +10 µC and a charge of +10 µC are 60 cm apart. Point P lies on the line between them, 36 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +10 µCq2 = +10 µCr1 = 36 cmr2 = 24 cm
E = N/C
5.Hard
+ + + + + +− − − − − −e⁻2.5 × 10⁷ m/s10 cmE = 2500 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 2.5 × 10⁷ m/s. The plates are 10 cm long and the field between them is 2500 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 = 2.5 × 10⁷ m/sL = 10 cmE = 2500 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
4 cm6 cm+q1​ = +4 µC+q3​ = +4 µC+q2​ = +10 µC

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

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

Answer key

  1. 1. E = 3996 N/C
  2. 2. r = 84.81 cm
  3. 3. x = 14.49 cm
  4. 4. E = 867091 N/C
  5. 5. y = 3.517 mm
  6. 6. F = 134.4 N

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