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
−−1 µCPr = 15 cm

Find the magnitude of the electric field E at a distance of 15 cm from a point charge of −1 µC. Use k = 8.99 × 10⁹ N·m²/C².

q = −1 µCr = 15 cm
E = N/C
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 38 N. The first charge is halved and the distance between the charges is doubled. Find the new force F′.

F = 38 Nq₁′ = 0.5·q₁r′ = 2·r
F′ = N
3.Medium
++3 µC++5 µCE = 080 cm

Charges of +3 µC and +5 µC are 80 cm apart. At what distance x from the +3 µC charge, on the line between them, is the electric field zero?

q1 = +3 µCq2 = +5 µCd = 80 cm
x = cm
4.Medium
−−8 µC++10 µC++4 µC4 cm + 6 cm

Three point charges lie on a straight line: −8 µC on the left, +4 µC on the right 10 cm away, and +10 µC between them, 4 cm from the left charge. Find the magnitude of the net electric force F on the middle charge. Use k = 8.99 × 10⁹ N·m²/C².

qL = −8 µCqR = +4 µCqM = +10 µCrL = 4 cmrR = 6 cm
F = N
5.Hard
++P2 × 4 cm12 cm+1 µC+1 µC

Charges of +1 µC and +1 µC are 8 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 = 8 cmh = 12 cm
E = N/C
6.Hard
6 cm6 cm+q1​ = +3 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 = 3 µC is 6 cm from it along one side and q₂ = 2 µC is 6 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 3 µCq2 = 2 µCq3 = 3 µCr13 = 6 cmr23 = 6 cm
F = N

Answer key

  1. 1. E = 399556 N/C
  2. 2. F′ = 4.75 N
  3. 3. x = 34.92 cm
  4. 4. F = 549.4 N
  5. 5. E = 1.066 × 10⁶ N/C
  6. 6. F = 27.01 N

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