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
++8 µC++5 µCr = ?

Point charges of +8 µC and +5 µC exert a force of 2 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 = 2 N
r = cm
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 58 N. The first charge is made four times as large and the distance between the charges is tripled. Find the new force F′.

F = 58 Nq₁′ = 4·q₁r′ = 3·r
F′ = N
3.Medium
++2 µC++5 µCP20 cm

A charge of +2 µC and a charge of +5 µC are 20 cm apart. Point P lies on the line between them, 5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +2 µCq2 = +5 µCr1 = 5 cmr2 = 15 cm
E = N/C
4.Medium
++4 µC++10 µCP60 cm

A charge of +4 µC and a charge of +10 µC are 60 cm apart. Point P lies on the line between them, 45 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +4 µCq2 = +10 µCr1 = 45 cmr2 = 15 cm
E = N/C
5.Hard
3 cm6 cm+q1​ = +10 µC+q3​ = +8 µC+q2​ = +10 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 8 µC is at the right-angle corner, q₁ = 10 µC is 3 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 = 10 µCq2 = 10 µCq3 = 8 µCr13 = 3 cmr23 = 6 cm
F = N
6.Hard
+−P2 × 6 cm12 cm+1 µC−1 µC

Charges of +1 µC and −1 µC are 12 cm apart. Point P lies 12 cm from the midpoint between them, on the perpendicular bisector. Find the magnitude of the electric field E at P. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +1 µCq2 = −1 µCd = 12 cmh = 12 cm
E = N/C

Answer key

  1. 1. r = 42.4 cm
  2. 2. F′ = 25.78 N
  3. 3. E = 5.194 × 10⁶ N/C
  4. 4. E = 3.818 × 10⁶ N/C
  5. 5. F = 823.7 N
  6. 6. E = 446717 N/C

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