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 = 25 cm

Two point charges of +8 µC and +5 µC are 25 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = +5 µCr = 25 cm
F = N
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 28 N. The first charge is tripled and the distance between the charges is doubled. Find the new force F′.

F = 28 Nq₁′ = 3·q₁r′ = 2·r
F′ = N
3.Medium
++5 µC−−3 µCP50 cm

A charge of +5 µC and a charge of −3 µC are 50 cm apart. Point P lies on the line between them, 30 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +5 µCq2 = −3 µCr1 = 30 cmr2 = 20 cm
E = N/C
4.Medium
++8 µC−−6 µCP50 cm

A charge of +8 µC and a charge of −6 µC are 50 cm apart. Point P lies on the line between them, 25 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +8 µCq2 = −6 µCr1 = 25 cmr2 = 25 cm
E = N/C
5.Hard
3 cm6 cm+q1​ = +1 µC+q3​ = +1 µC+q2​ = +3 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 1 µC is at the right-angle corner, q₁ = 1 µC is 3 cm from it along one side and q₂ = 3 µC is 6 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 1 µCq2 = 3 µCq3 = 1 µCr13 = 3 cmr23 = 6 cm
F = N
6.Hard
+−P2 × 10 cm3 cm+2 µC−2 µC

Charges of +2 µC and −2 µC are 20 cm apart. Point P lies 3 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 = +2 µCq2 = −2 µCd = 20 cmh = 3 cm
E = N/C

Answer key

  1. 1. F = 5.754 N
  2. 2. F′ = 21 N
  3. 3. E = 1.174 × 10⁶ N/C
  4. 4. E = 2.014 × 10⁶ N/C
  5. 5. F = 12.49 N
  6. 6. E = 3.16 × 10⁶ N/C

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