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++2 µCr = 15 cm

Two point charges of −10 µC and +2 µC are 15 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −10 µCq2 = +2 µCr = 15 cm
F = N
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 54 N. The first charge is tripled and the distance between the charges is doubled. Find the new force F′.

F = 54 Nq₁′ = 3·q₁r′ = 2·r
F′ = N
3.Medium
++10 µC++8 µCP30 cm

A charge of +10 µC and a charge of +8 µC are 30 cm apart. Point P lies on the line between them, 22.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +10 µCq2 = +8 µCr1 = 22.5 cmr2 = 7.5 cm
E = N/C
4.Medium
++5 µC−−6 µCP20 cm

A charge of +5 µC and a charge of −6 µC are 20 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 = +5 µCq2 = −6 µCr1 = 15 cmr2 = 5 cm
E = N/C
5.Hard
+ + + + + +− − − − − −e⁻3.5 × 10⁷ m/s6 cmE = 3700 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 3.5 × 10⁷ m/s. The plates are 6 cm long and the field between them is 3700 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 = 3.5 × 10⁷ m/sL = 6 cmE = 3700 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
4 cm10 cm+q1​ = +4 µC+q3​ = +2 µC+q2​ = +4 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 2 µC is at the right-angle corner, q₁ = 4 µC is 4 cm from it along one side and q₂ = 4 µC is 10 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 4 µCq2 = 4 µCq3 = 2 µCr13 = 4 cmr23 = 10 cm
F = N

Answer key

  1. 1. F = 7.991 N
  2. 2. F′ = 40.5 N
  3. 3. E = 1.101 × 10⁷ N/C
  4. 4. E = 2.357 × 10⁷ N/C
  5. 5. y = 0.9562 mm
  6. 6. F = 45.52 N

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