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++10 µCr = ?

Point charges of +8 µC and +10 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 = +8 µCq2 = +10 µCF = 5 N
r = cm
2.Easy
−−4 µC−−8 µCr = 2 cm

Two point charges of −4 µC and −8 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 = −8 µCr = 2 cm
F = N
3.Medium
++2 µC++10 µCE = 010 cm

Charges of +2 µC and +10 µC are 10 cm apart. At what distance x from the +2 µC charge, on the line between them, is the electric field zero?

q1 = +2 µCq2 = +10 µCd = 10 cm
x = cm
4.Medium
++8 µC++8 µCP50 cm

A charge of +8 µC and a charge of +8 µC are 50 cm apart. Point P lies on the line between them, 12.5 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +8 µCq2 = +8 µCr1 = 12.5 cmr2 = 37.5 cm
E = N/C
5.Hard
+ + + + + +− − − − − −e⁻1 × 10⁷ m/s6 cmE = 3300 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 1 × 10⁷ m/s. The plates are 6 cm long and the field between them is 3300 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 = 6 cmE = 3300 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
L = 80 cm10°qq

Two identical small balls, each of mass 1 g, hang from the same point on insulating threads 80 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 = 1 gL = 80 cmθ = 10°g = 9.81 m/s²
q = nC

Answer key

  1. 1. r = 37.93 cm
  2. 2. F = 719.2 N
  3. 3. x = 3.09 cm
  4. 4. E = 4.091 × 10⁶ N/C
  5. 5. y = 10.45 mm
  6. 6. q = 121.9 nC

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