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
−−2 µC++5 µCr = 3 cm

Two point charges of −2 µC and +5 µC are 3 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −2 µCq2 = +5 µCr = 3 cm
F = N
2.Easy
++10 µC−−6 µCr = ?

Point charges of +10 µC and −6 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 = +10 µCq2 = −6 µCF = 5 N
r = cm
3.Medium
++3 µC++5 µCE = 080 cm

Charges of +3 µC and +5 µC are 80 cm apart. At what distance x from the +3 µC charge, on the line between them, is the electric field zero?

q1 = +3 µCq2 = +5 µCd = 80 cm
x = cm
4.Medium
++8 µC++5 µCE = 080 cm

Charges of +8 µC and +5 µC are 80 cm apart. At what distance x from the +8 µC charge, on the line between them, is the electric field zero?

q1 = +8 µCq2 = +5 µCd = 80 cm
x = cm
5.Hard
+ + + + + +− − − − − −e⁻3.5 × 10⁷ m/s8 cmE = 4900 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 3.5 × 10⁷ m/s. The plates are 8 cm long and the field between them is 4900 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 = 3.5 × 10⁷ m/sL = 8 cmE = 4900 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
L = 100 cm5°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 5° 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 = 5°g = 9.81 m/s²
q = nC

Answer key

  1. 1. F = 99.89 N
  2. 2. r = 32.85 cm
  3. 3. x = 34.92 cm
  4. 4. x = 44.68 cm
  5. 5. y = 2.251 mm
  6. 6. q = 170.3 nC

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