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
+q₁+q₂r

Two point charges repel each other with a force of 40 N. The first charge is halved and the distance between the charges is tripled. Find the new force F′.

F = 40 Nq₁′ = 0.5·q₁r′ = 3·r
F′ = N
2.Easy
−−3 µC++4 µCr = 15 cm

Two point charges of −3 µC and +4 µC are 15 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −3 µCq2 = +4 µCr = 15 cm
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
++6 µC++10 µCP40 cm

A charge of +6 µC and a charge of +10 µC are 40 cm apart. Point P lies on the line between them, 10 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +6 µCq2 = +10 µCr1 = 10 cmr2 = 30 cm
E = N/C
5.Hard
4 cm8 cm+q1​ = +5 µC+q3​ = +6 µC+q2​ = +5 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 6 µC is at the right-angle corner, q₁ = 5 µC is 4 cm from it along one side and q₂ = 5 µC is 8 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 5 µCq2 = 5 µCq3 = 6 µCr13 = 4 cmr23 = 8 cm
F = N
6.Hard
++P2 × 4 cm10 cm+4 µC+4 µC

Charges of +4 µC and +4 µC are 8 cm apart. Point P lies 10 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 = +4 µCq2 = +4 µCd = 8 cmh = 10 cm
E = N/C

Answer key

  1. 1. F′ = 2.222 N
  2. 2. F = 4.795 N
  3. 3. E = 174806 N/C
  4. 4. E = 4.395 × 10⁶ N/C
  5. 5. F = 173.8 N
  6. 6. E = 5.757 × 10⁶ N/C

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