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−−1 µCr = 10 cm

Two point charges of −8 µC and −1 µC are 10 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −8 µCq2 = −1 µCr = 10 cm
F = N
2.Easy
++3 µC++8 µCr = ?

Point charges of +3 µC and +8 µC exert a force of 20 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = +8 µCF = 20 N
r = cm
3.Medium
++4 µC++5 µCP50 cm

A charge of +4 µC and a charge of +5 µC are 50 cm apart. Point P lies on the line between them, 12.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +4 µCq2 = +5 µCr1 = 12.5 cmr2 = 37.5 cm
E = N/C
4.Medium
++3 µC++6 µCP50 cm

A charge of +3 µC and a charge of +6 µC are 50 cm apart. Point P lies on the line between them, 12.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +3 µCq2 = +6 µCr1 = 12.5 cmr2 = 37.5 cm
E = N/C
5.Hard
+ + + + + +− − − − − −e⁻1 × 10⁷ m/s3 cmE = 2100 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 1 × 10⁷ m/s. The plates are 3 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 = 1 × 10⁷ m/sL = 3 cmE = 2100 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
8 cm10 cm+q1​ = +1 µC+q3​ = +8 µC+q2​ = +10 µC

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

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

Answer key

  1. 1. F = 7.192 N
  2. 2. r = 10.39 cm
  3. 3. E = 1.982 × 10⁶ N/C
  4. 4. E = 1.343 × 10⁶ N/C
  5. 5. y = 1.662 mm
  6. 6. F = 72.79 N

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