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
−−4 µC−−5 µCr = 2 cm

Two point charges of −4 µC and −5 µC are 2 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −4 µCq2 = −5 µCr = 2 cm
F = N
2.Easy
−−8 µC−−4 µCr = 5 cm

Two point charges of −8 µC and −4 µC are 5 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −8 µCq2 = −4 µCr = 5 cm
F = N
3.Medium
++10 µC++4 µCP20 cm

A charge of +10 µC and a charge of +4 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 = +10 µCq2 = +4 µCr1 = 5 cmr2 = 15 cm
E = N/C
4.Medium
++3 µC−−10 µC++5 µC24 cm + 16 cm

Three point charges lie on a straight line: +3 µC on the left, +5 µC on the right 40 cm away, and −10 µC between them, 24 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 = +3 µCqR = +5 µCqM = −10 µCrL = 24 cmrR = 16 cm
F = N
5.Hard
+ + + + + +− − − − − −e⁻2.5 × 10⁷ m/s8 cmE = 3400 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 8 cm long and the field between them is 3400 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 = 8 cmE = 3400 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
L = 50 cm15°qq

Two identical small balls, each of mass 3 g, hang from the same point on insulating threads 50 cm long. They are given equal charges and each thread settles at 15° 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 = 3 gL = 50 cmθ = 15°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 449.5 N
  2. 2. F = 115.1 N
  3. 3. E = 3.436 × 10⁷ N/C
  4. 4. F = 12.88 N
  5. 5. y = 3.062 mm
  6. 6. q = 242.4 nC

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