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
++3 µC++2 µCr = ?

Point charges of +3 µC and +2 µC exert a force of 5 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 = +2 µCF = 5 N
r = cm
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 22 N. The first charge is halved and the distance between the charges is made four times as large. Find the new force F′.

F = 22 Nq₁′ = 0.5·q₁r′ = 4·r
F′ = N
3.Medium
++2 µC−−3 µCP60 cm

A charge of +2 µC and a charge of −3 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 = +2 µCq2 = −3 µCr1 = 15 cmr2 = 45 cm
E = N/C
4.Medium
++2 µC−−10 µCP10 cm

A charge of +2 µC and a charge of −10 µC are 10 cm apart. Point P lies on the line between them, 2.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +2 µCq2 = −10 µCr1 = 2.5 cmr2 = 7.5 cm
E = N/C
5.Hard
+ + + + + +− − − − − −e⁻2.5 × 10⁷ m/s4 cmE = 4100 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 2.5 × 10⁷ m/s. The plates are 4 cm long and the field between them is 4100 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 = 2.5 × 10⁷ m/sL = 4 cmE = 4100 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
5 cm10 cm+q1​ = +1 µC+q3​ = +3 µC+q2​ = +5 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 3 µC is at the right-angle corner, q₁ = 1 µC is 5 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 = 1 µCq2 = 5 µCq3 = 3 µCr13 = 5 cmr23 = 10 cm
F = N

Answer key

  1. 1. r = 10.39 cm
  2. 2. F′ = 0.6875 N
  3. 3. E = 932296 N/C
  4. 4. E = 4.475 × 10⁷ N/C
  5. 5. y = 0.923 mm
  6. 6. F = 17.27 N

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