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
++2 µC++6 µCr = 25 cm

Two point charges of +2 µC and +6 µC are 25 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +2 µCq2 = +6 µCr = 25 cm
F = N
2.Easy
+ + + + + +− − − − − −e⁻E = 400 N/C

A proton (charge 1.602 × 10⁻¹⁹ C, mass 1.673 × 10⁻²⁷ kg) is in a uniform electric field of 400 N/C. Ignoring gravity, find the magnitude of its acceleration a.

E = 400 N/C|q| = 1.602 × 10⁻¹⁹ Cm = 1.673 × 10⁻²⁷ kg
a = m/s²
3.Medium
−−2 µC−−3 µC−−5 µC5 cm + 15 cm

Three point charges lie on a straight line: −2 µC on the left, −5 µC on the right 20 cm away, and −3 µC between them, 5 cm from the left charge. Find the magnitude of the net electric force F on the middle charge. Use k = 8.99 × 10⁹ N·m²/C².

qL = −2 µCqR = −5 µCqM = −3 µCrL = 5 cmrR = 15 cm
F = N
4.Medium
−−1 µC++4 µC++2 µC6 cm + 4 cm

Three point charges lie on a straight line: −1 µC on the left, +2 µC on the right 10 cm away, and +4 µC between them, 6 cm from the left charge. Find the magnitude of the net electric force F on the middle charge. Use k = 8.99 × 10⁹ N·m²/C².

qL = −1 µCqR = +2 µCqM = +4 µCrL = 6 cmrR = 4 cm
F = N
5.Hard
+ + + + + +− − − − − −e⁻1.5 × 10⁷ m/s6 cmE = 300 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 6 cm long and the field between them is 300 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 = 6 cmE = 300 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
6 cm10 cm+q1​ = +2 µC+q3​ = +2 µC+q2​ = +5 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 2 µC is at the right-angle corner, q₁ = 2 µC is 6 cm from it along one side and q₂ = 5 µC is 10 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 2 µCq2 = 5 µCq3 = 2 µCr13 = 6 cmr23 = 10 cm
F = N

Answer key

  1. 1. F = 1.726 N
  2. 2. a = 3.83 × 10¹⁰ m/s²
  3. 3. F = 15.58 N
  4. 4. F = 54.94 N
  5. 5. y = 0.4221 mm
  6. 6. F = 13.44 N

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