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 µC++8 µCr = ?

Point charges of +3 µC and +8 µC exert a force of 50 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = +8 µCF = 50 N
r = cm
2.Easy
+ + + + + +− − − − − −e⁻E = 4800 N/C

A proton (charge 1.602 × 10⁻¹⁹ C, mass 1.673 × 10⁻²⁷ kg) is in a uniform electric field of 4800 N/C. Ignoring gravity, find the magnitude of its acceleration a.

E = 4800 N/C|q| = 1.602 × 10⁻¹⁹ Cm = 1.673 × 10⁻²⁷ kg
a = m/s²
3.Medium
++5 µC−−5 µCP30 cm

A charge of +5 µC and a charge of −5 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 = +5 µCq2 = −5 µCr1 = 22.5 cmr2 = 7.5 cm
E = N/C
4.Medium
++10 µC−−1 µCP40 cm

A charge of +10 µC and a charge of −1 µC are 40 cm apart. Point P lies on the line between them, 16 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +10 µCq2 = −1 µCr1 = 16 cmr2 = 24 cm
E = N/C
5.Hard
6 cm5 cm+q1​ = +6 µC+q3​ = +1 µC+q2​ = +1 µC

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

q1 = 6 µCq2 = 1 µCq3 = 1 µCr13 = 6 cmr23 = 5 cm
F = N
6.Hard
4 cm8 cm+q1​ = +8 µC+q3​ = +3 µC+q2​ = +2 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 3 µC is at the right-angle corner, q₁ = 8 µC is 4 cm from it along one side and q₂ = 2 µC is 8 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 8 µCq2 = 2 µCq3 = 3 µCr13 = 4 cmr23 = 8 cm
F = N

Answer key

  1. 1. r = 6.569 cm
  2. 2. a = 4.596 × 10¹¹ m/s²
  3. 3. E = 8.879 × 10⁶ N/C
  4. 4. E = 3.668 × 10⁶ N/C
  5. 5. F = 15.41 N
  6. 6. F = 135.1 N

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