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++4 µCr = ?

Point charges of +8 µC and +4 µC exert a force of 8 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = +4 µCF = 8 N
r = cm
2.Easy
−−1 µC−−10 µCr = 3 cm

Two point charges of −1 µC and −10 µC are 3 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −1 µCq2 = −10 µCr = 3 cm
F = N
3.Medium
++2 µC−−6 µCP20 cm

A charge of +2 µC and a charge of −6 µC are 20 cm apart. Point P lies on the line between them, 5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +2 µCq2 = −6 µCr1 = 5 cmr2 = 15 cm
E = N/C
4.Medium
−−5 µC−−5 µC++3 µC2.5 cm + 7.5 cm

Three point charges lie on a straight line: −5 µC on the left, +3 µC on the right 10 cm away, and −5 µC between them, 2.5 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 = −5 µCqR = +3 µCqM = −5 µCrL = 2.5 cmrR = 7.5 cm
F = N
5.Hard
L = 100 cm10°qq

Two identical small balls, each of mass 10 g, hang from the same point on insulating threads 100 cm long. They are given equal charges and each thread settles at 10° from the vertical. Use g = 9.81 m/s². Find the charge q on each ball in nC. Use k = 8.99 × 10⁹ N·m²/C².

m = 10 gL = 100 cmθ = 10°g = 9.81 m/s²
q = nC
6.Hard
+ + + + + +− − − − − −e⁻2 × 10⁷ m/s6 cmE = 1900 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 2 × 10⁷ m/s. The plates are 6 cm long and the field between them is 1900 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 × 10⁷ m/sL = 6 cmE = 1900 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. r = 18.96 cm
  2. 2. F = 99.89 N
  3. 3. E = 9.589 × 10⁶ N/C
  4. 4. F = 383.6 N
  5. 5. q = 481.7 nC
  6. 6. y = 1.504 mm

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