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
++10 µC++8 µCr = 8 cm

Two point charges of +10 µC and +8 µC are 8 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +10 µCq2 = +8 µCr = 8 cm
F = N
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 4 N. The first charge is made four times as large and the distance between the charges is tripled. Find the new force F′.

F = 4 Nq₁′ = 4·q₁r′ = 3·r
F′ = N
3.Medium
++10 µC−−1 µCP50 cm

A charge of +10 µC and a charge of −1 µC are 50 cm apart. Point P lies on the line between them, 12.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +10 µCq2 = −1 µCr1 = 12.5 cmr2 = 37.5 cm
E = N/C
4.Medium
++4 µC++1 µCP10 cm

A charge of +4 µC and a charge of +1 µC are 10 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 = +4 µCq2 = +1 µCr1 = 5 cmr2 = 5 cm
E = N/C
5.Hard
L = 50 cm5°qq

Two identical small balls, each of mass 3 g, hang from the same point on insulating threads 50 cm long. They are given equal charges and each thread settles at 5° from the vertical. Use g = 9.81 m/s². Find the charge q on each ball in nC. Use k = 8.99 × 10⁹ N·m²/C².

m = 3 gL = 50 cmθ = 5°g = 9.81 m/s²
q = nC
6.Hard
L = 30 cm10°qq

Two identical small balls, each of mass 10 g, hang from the same point on insulating threads 30 cm long. They are given equal charges and each thread settles at 10° from the vertical. Use g = 9.81 m/s². Find the charge q on each ball in nC. Use k = 8.99 × 10⁹ N·m²/C².

m = 10 gL = 30 cmθ = 10°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 112.4 N
  2. 2. F′ = 1.778 N
  3. 3. E = 5.818 × 10⁶ N/C
  4. 4. E = 1.079 × 10⁷ N/C
  5. 5. q = 46.64 nC
  6. 6. q = 144.5 nC

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