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 µC++10 µCr = ?

Point charges of +1 µC and +10 µC exert a force of 50 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +1 µCq2 = +10 µCF = 50 N
r = cm
2.Easy
++3 µC−−3 µCr = 30 cm

Two point charges of +3 µC and −3 µC are 30 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = −3 µCr = 30 cm
F = N
3.Medium
++3 µC++1 µCr = 10 cm

Two identical small metal spheres carry charges of +3 µC and +1 µC. They are touched together and then put back 10 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = +1 µCr = 10 cm
F = N
4.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
5.Hard
+−P2 × 8 cm6 cm+5 µC−5 µC

Charges of +5 µC and −5 µC are 16 cm apart. Point P lies 6 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 = +5 µCq2 = −5 µCd = 16 cmh = 6 cm
E = N/C
6.Hard
4 cm6 cm+q1​ = +8 µC+q3​ = +6 µC+q2​ = +10 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 6 µC is at the right-angle corner, q₁ = 8 µC is 4 cm from it along one side and q₂ = 10 µC is 6 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 8 µCq2 = 10 µCq3 = 6 µCr13 = 4 cmr23 = 6 cm
F = N

Answer key

  1. 1. r = 4.24 cm
  2. 2. F = 0.899 N
  3. 3. F = 3.596 N
  4. 4. x = 34.92 cm
  5. 5. E = 7.192 × 10⁶ N/C
  6. 6. F = 308.5 N

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