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−−10 µCr = ?

Point charges of +8 µC and −10 µC exert a force of 10 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = −10 µCF = 10 N
r = cm
2.Easy
++1 µC−−2 µCr = 6 cm

Two point charges of +1 µC and −2 µC are 6 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +1 µCq2 = −2 µCr = 6 cm
F = N
3.Medium
−−3 µC++1 µCr = 20 cm

Two identical small metal spheres carry charges of −3 µC and +1 µC. They are touched together and then put back 20 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 = 20 cm
F = N
4.Medium
++4 µC++5 µCE = 050 cm

Charges of +4 µC and +5 µC are 50 cm apart. At what distance x from the +4 µC charge, on the line between them, is the electric field zero?

q1 = +4 µCq2 = +5 µCd = 50 cm
x = cm
5.Hard
+ + + + + +− − − − − −e⁻3 × 10⁷ m/s5 cmE = 2600 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 3 × 10⁷ m/s. The plates are 5 cm long and the field between them is 2600 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 = 5 cmE = 2600 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
6 cm8 cm+q1​ = +4 µC+q3​ = +3 µC+q2​ = +4 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 3 µC is at the right-angle corner, q₁ = 4 µC is 6 cm from it along one side and q₂ = 4 µC is 8 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 4 µCq2 = 4 µCq3 = 3 µCr13 = 6 cmr23 = 8 cm
F = N

Answer key

  1. 1. r = 26.82 cm
  2. 2. F = 4.994 N
  3. 3. F = 0.2247 N
  4. 4. x = 23.61 cm
  5. 5. y = 0.6351 mm
  6. 6. F = 34.38 N

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