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
+q₁+q₂r

Two point charges repel each other with a force of 10 N. The first charge is halved and the distance between the charges is doubled. Find the new force F′.

F = 10 Nq₁′ = 0.5·q₁r′ = 2·r
F′ = N
2.Easy
−−5 µC−−4 µCr = 30 cm

Two point charges of −5 µC and −4 µC are 30 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −5 µCq2 = −4 µCr = 30 cm
F = N
3.Medium
++6 µC−−10 µCP30 cm

A charge of +6 µC and a charge of −10 µC are 30 cm apart. Point P lies on the line between them, 7.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +6 µCq2 = −10 µCr1 = 7.5 cmr2 = 22.5 cm
E = N/C
4.Medium
++8 µC−−4 µC++3 µC12 cm + 18 cm

Three point charges lie on a straight line: +8 µC on the left, +3 µC on the right 30 cm away, and −4 µC between them, 12 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 = +8 µCqR = +3 µCqM = −4 µCrL = 12 cmrR = 18 cm
F = N
5.Hard
10 cm10 cm+q1​ = +2 µC+q3​ = +6 µC+q2​ = +2 µC

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

q1 = 2 µCq2 = 2 µCq3 = 6 µCr13 = 10 cmr23 = 10 cm
F = N
6.Hard
+ + + + + +− − − − − −e⁻1 × 10⁷ m/s2 cmE = 4500 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 1 × 10⁷ m/s. The plates are 2 cm long and the field between them is 4500 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 = 2 cmE = 4500 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. F′ = 1.25 N
  2. 2. F = 1.998 N
  3. 3. E = 1.137 × 10⁷ N/C
  4. 4. F = 16.65 N
  5. 5. F = 15.26 N
  6. 6. y = 1.583 mm

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