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
++6 µC−−3 µCr = 12 cm

Two point charges of +6 µC and −3 µC are 12 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +6 µCq2 = −3 µCr = 12 cm
F = N
2.Easy
++4 µC++4 µCr = 2 cm

Two point charges of +4 µC and +4 µC are 2 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +4 µCq2 = +4 µCr = 2 cm
F = N
3.Medium
++3 µC++10 µCP10 cm

A charge of +3 µC and a charge of +10 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 = +3 µCq2 = +10 µCr1 = 5 cmr2 = 5 cm
E = N/C
4.Medium
++4 µC−−10 µCr = 15 cm

Two identical small metal spheres carry charges of +4 µC and −10 µC. They are touched together and then put back 15 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +4 µCq2 = −10 µCr = 15 cm
F = N
5.Hard
+ + + + + +− − − − − −e⁻3 × 10⁷ m/s8 cmE = 5000 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 3 × 10⁷ m/s. The plates are 8 cm long and the field between them is 5000 N/C. Electron charge 1.602 × 10⁻¹⁹ C, mass 9.109 × 10⁻³¹ kg; ignore gravity. How far y is it deflected sideways when it leaves the plates? Give the answer in mm.

v₀ = 3 × 10⁷ m/sL = 8 cmE = 5000 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
8 cm10 cm+q1​ = +8 µC+q3​ = +10 µC+q2​ = +1 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 10 µC is at the right-angle corner, q₁ = 8 µC is 8 cm from it along one side and q₂ = 1 µC is 10 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 8 µCq2 = 1 µCq3 = 10 µCr13 = 8 cmr23 = 10 cm
F = N

Answer key

  1. 1. F = 11.24 N
  2. 2. F = 359.6 N
  3. 3. E = 2.517 × 10⁷ N/C
  4. 4. F = 3.596 N
  5. 5. y = 3.127 mm
  6. 6. F = 112.7 N

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