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 = ?

Point charges of +10 µC and +2 µC exert a force of 2 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +10 µCq2 = +2 µCF = 2 N
r = cm
2.Easy
−−10 µC++5 µCr = 4 cm

Two point charges of −10 µC and +5 µC are 4 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −10 µCq2 = +5 µCr = 4 cm
F = N
3.Medium
−−1 µC−−5 µCr = 10 cm

Two identical small metal spheres carry charges of −1 µC and −5 µC. They are touched together and then put back 10 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −1 µCq2 = −5 µCr = 10 cm
F = N
4.Medium
++1 µC−−10 µCP50 cm

A charge of +1 µC and a charge of −10 µC are 50 cm apart. Point P lies on the line between them, 37.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +1 µCq2 = −10 µCr1 = 37.5 cmr2 = 12.5 cm
E = N/C
5.Hard
L = 50 cm10°qq

Two identical small balls, each of mass 2 g, hang from the same point on insulating threads 50 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 = 2 gL = 50 cmθ = 10°g = 9.81 m/s²
q = nC
6.Hard
+ + + + + +− − − − − −e⁻4 × 10⁷ m/s4 cmE = 4600 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 4 × 10⁷ m/s. The plates are 4 cm long and the field between them is 4600 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 = 4 × 10⁷ m/sL = 4 cmE = 4600 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. r = 29.98 cm
  2. 2. F = 280.9 N
  3. 3. F = 8.091 N
  4. 4. E = 5.818 × 10⁶ N/C
  5. 5. q = 107.7 nC
  6. 6. y = 0.4045 mm

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