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−−10 µCr = 20 cm

Two point charges of −10 µC and −10 µC are 20 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −10 µCq2 = −10 µCr = 20 cm
F = N
2.Easy
++5 µC−−8 µCr = 8 cm

Two point charges of +5 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 = +5 µCq2 = −8 µCr = 8 cm
F = N
3.Medium
++5 µC++1 µCE = 0100 cm

Charges of +5 µC and +1 µC are 100 cm apart. At what distance x from the +5 µC charge, on the line between them, is the electric field zero?

q1 = +5 µCq2 = +1 µCd = 100 cm
x = cm
4.Medium
−−4 µC++5 µCr = 5 cm

Two identical small metal spheres carry charges of −4 µC and +5 µC. They are touched together and then put back 5 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −4 µCq2 = +5 µCr = 5 cm
F = N
5.Hard
+ + + + + +− − − − − −e⁻1.5 × 10⁷ m/s3 cmE = 3000 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 1.5 × 10⁷ m/s. The plates are 3 cm long and the field between them is 3000 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 = 1.5 × 10⁷ m/sL = 3 cmE = 3000 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
10 cm3 cm+q1​ = +8 µC+q3​ = +3 µC+q2​ = +3 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 3 µC is at the right-angle corner, q₁ = 8 µC is 10 cm from it along one side and q₂ = 3 µC is 3 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 8 µCq2 = 3 µCq3 = 3 µCr13 = 10 cmr23 = 3 cm
F = N

Answer key

  1. 1. F = 22.47 N
  2. 2. F = 56.19 N
  3. 3. x = 69.1 cm
  4. 4. F = 0.899 N
  5. 5. y = 1.055 mm
  6. 6. F = 92.45 N

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