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

Two point charges of +8 µC and +4 µC are 4 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q₁ = +8 µCq₂ = +4 µCr = 4 cm

F = N

2.Easy

Two point charges of +3 µC and +6 µC are 4 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q₁ = +3 µCq₂ = +6 µCr = 4 cm

F = N

3.Medium

Charges of +8 µC and +3 µC are 10 cm apart. At what distance x from the +8 µC charge, on the line between them, is the electric field zero?

q₁ = +8 µCq₂ = +3 µCd = 10 cm

x = cm

4.Medium

Charges of +3 µC and +5 µC are 60 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 = 60 cm

x = cm

5.Hard

Three positive point charges sit at the corners of a right triangle: q₃ = 4 µC is at the right-angle corner, q₁ = 3 µC is 6 cm from it along one side and q₂ = 6 µC is 4 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q₁ = 3 µCq₂ = 6 µCq₃ = 4 µCr₁₃ = 6 cmr₂₃ = 4 cm

F = N

6.Hard

Two identical small balls, each of mass 3 g, hang from the same point on insulating threads 20 cm long. They are given equal charges and each thread settles at 8° 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 = 20 cmθ = 8°g = 9.81 m/s²

q = nC

Answer key

1. F = 179.8 N
2. F = 101.1 N
3. x = 6.202 cm
4. x = 26.19 cm
5. F = 138.1 N
6. q = 37.76 nC

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