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
++4 µC−−3 µCr = 10 cm

Two point charges of +4 µC and −3 µC are 10 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +4 µCq2 = −3 µCr = 10 cm
F = N
2.Easy
++5 µC++8 µCr = ?

Point charges of +5 µC and +8 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 = +5 µCq2 = +8 µCF = 50 N
r = cm
3.Medium
++10 µC−−2 µCP60 cm

A charge of +10 µC and a charge of −2 µC are 60 cm apart. Point P lies on the line between them, 15 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +10 µCq2 = −2 µCr1 = 15 cmr2 = 45 cm
E = N/C
4.Medium
++5 µC−−5 µCP60 cm

A charge of +5 µC and a charge of −5 µC are 60 cm apart. Point P lies on the line between them, 30 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +5 µCq2 = −5 µCr1 = 30 cmr2 = 30 cm
E = N/C
5.Hard
5 cm5 cm+q1​ = +3 µC+q3​ = +2 µC+q2​ = +1 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 2 µC is at the right-angle corner, q₁ = 3 µC is 5 cm from it along one side and q₂ = 1 µC is 5 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 3 µCq2 = 1 µCq3 = 2 µCr13 = 5 cmr23 = 5 cm
F = N
6.Hard
+ + + + + +− − − − − −e⁻4 × 10⁷ m/s6 cmE = 2100 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 4 × 10⁷ m/s. The plates are 6 cm long and the field between them is 2100 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 = 4 × 10⁷ m/sL = 6 cmE = 2100 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. F = 10.79 N
  2. 2. r = 8.481 cm
  3. 3. E = 4.084 × 10⁶ N/C
  4. 4. E = 998889 N/C
  5. 5. F = 22.74 N
  6. 6. y = 0.4155 mm

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