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 = 30 cm

Two point charges of +8 µC and +5 µC are 30 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 = 30 cm
F = N
2.Easy
+q₁+q₂r

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

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

A charge of +3 µC and a charge of +2 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 = +3 µCq2 = +2 µCr1 = 5 cmr2 = 15 cm
E = N/C
4.Medium
++6 µC++10 µCE = 060 cm

Charges of +6 µC and +10 µC are 60 cm apart. At what distance x from the +6 µC charge, on the line between them, is the electric field zero?

q1 = +6 µCq2 = +10 µCd = 60 cm
x = cm
5.Hard
+−P2 × 8 cm12 cm+6 µC−6 µC

Charges of +6 µC and −6 µC are 16 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 = +6 µCq2 = −6 µCd = 16 cmh = 12 cm
E = N/C
6.Hard
5 cm10 cm+q1​ = +2 µC+q3​ = +1 µC+q2​ = +10 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 1 µC is at the right-angle corner, q₁ = 2 µC is 5 cm from it along one side and q₂ = 10 µC is 10 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 2 µCq2 = 10 µCq3 = 1 µCr13 = 5 cmr23 = 10 cm
F = N

Answer key

  1. 1. F = 3.996 N
  2. 2. F′ = 10.88 N
  3. 3. E = 9.989 × 10⁶ N/C
  4. 4. x = 26.19 cm
  5. 5. E = 2.877 × 10⁶ N/C
  6. 6. F = 11.51 N

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