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
++6 µC−−4 µCr = 3 cm

Two point charges of +6 µC and −4 µC are 3 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +6 µCq2 = −4 µCr = 3 cm
F = N
2.Easy
++2 µC−−3 µCr = ?

Point charges of +2 µC and −3 µC exert a force of 0.5 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +2 µCq2 = −3 µCF = 0.5 N
r = cm
3.Medium
−−10 µC++3 µC−−3 µC24 cm + 16 cm

Three point charges lie on a straight line: −10 µC on the left, −3 µC on the right 40 cm away, and +3 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 = −10 µCqR = −3 µCqM = +3 µCrL = 24 cmrR = 16 cm
F = N
4.Medium
++4 µC++5 µCE = 0100 cm

Charges of +4 µC and +5 µC are 100 cm apart. At what distance x from the +4 µC charge, on the line between them, is the electric field zero?

q1 = +4 µCq2 = +5 µCd = 100 cm
x = cm
5.Hard
+ + + + + +− − − − − −e⁻1 × 10⁷ m/s5 cmE = 2700 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 1 × 10⁷ m/s. The plates are 5 cm long and the field between them is 2700 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 = 5 cmE = 2700 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
10 cm6 cm+q1​ = +8 µC+q3​ = +6 µC+q2​ = +10 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 6 µC is at the right-angle corner, q₁ = 8 µC is 10 cm from it along one side and q₂ = 10 µC is 6 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 8 µCq2 = 10 µCq3 = 6 µCr13 = 10 cmr23 = 6 cm
F = N

Answer key

  1. 1. F = 239.7 N
  2. 2. r = 32.85 cm
  3. 3. F = 1.522 N
  4. 4. x = 47.21 cm
  5. 5. y = 5.936 mm
  6. 6. F = 155.9 N

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