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
++1 µC++2 µCr = ?

Point charges of +1 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 = +1 µCq2 = +2 µCF = 2 N
r = cm
2.Easy
++1 µC++1 µCr = ?

Point charges of +1 µC and +1 µC exert a force of 10 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +1 µCq2 = +1 µCF = 10 N
r = cm
3.Medium
−−6 µC−−6 µC++5 µC24 cm + 16 cm

Three point charges lie on a straight line: −6 µC on the left, +5 µC on the right 40 cm away, and −6 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 = −6 µCqR = +5 µCqM = −6 µCrL = 24 cmrR = 16 cm
F = N
4.Medium
++10 µC−−3 µCr = 50 cm

Two identical small metal spheres carry charges of +10 µC and −3 µC. They are touched together and then put back 50 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +10 µCq2 = −3 µCr = 50 cm
F = N
5.Hard
+ + + + + +− − − − − −e⁻3 × 10⁷ m/s10 cmE = 3200 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 3 × 10⁷ m/s. The plates are 10 cm long and the field between them is 3200 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 × 10⁷ m/sL = 10 cmE = 3200 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
+ + + + + +− − − − − −e⁻5 × 10⁷ m/s5 cmE = 3500 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 5 × 10⁷ m/s. The plates are 5 cm long and the field between them is 3500 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 = 5 × 10⁷ m/sL = 5 cmE = 3500 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. r = 9.482 cm
  2. 2. r = 2.998 cm
  3. 3. F = 16.15 N
  4. 4. F = 0.4405 N
  5. 5. y = 3.127 mm
  6. 6. y = 0.3078 mm

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