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
−−4 µC−−6 µCr = 12 cm

Two point charges of −4 µC and −6 µC are 12 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −4 µCq2 = −6 µCr = 12 cm
F = N
2.Easy
++6 µC++10 µCr = ?

Point charges of +6 µC and +10 µC exert a force of 20 N on each other. How far apart r are they? Give the answer in cm. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +6 µCq2 = +10 µCF = 20 N
r = cm
3.Medium
++6 µC++3 µCE = 050 cm

Charges of +6 µC and +3 µC are 50 cm apart. At what distance x from the +6 µC charge, on the line between them, is the electric field zero?

q1 = +6 µCq2 = +3 µCd = 50 cm
x = cm
4.Medium
−−10 µC++8 µC++2 µC7.5 cm + 2.5 cm

Three point charges lie on a straight line: −10 µC on the left, +2 µC on the right 10 cm away, and +8 µC between them, 7.5 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 = +2 µCqM = +8 µCrL = 7.5 cmrR = 2.5 cm
F = N
5.Hard
6 cm8 cm+q1​ = +1 µC+q3​ = +1 µC+q2​ = +8 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 1 µC is at the right-angle corner, q₁ = 1 µC is 6 cm from it along one side and q₂ = 8 µC is 8 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 1 µCq2 = 8 µCq3 = 1 µCr13 = 6 cmr23 = 8 cm
F = N
6.Hard
+ + + + + +− − − − − −e⁻4 × 10⁷ m/s4 cmE = 4800 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 4800 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 = 4800 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. F = 14.98 N
  2. 2. r = 16.42 cm
  3. 3. x = 29.29 cm
  4. 4. F = 358 N
  5. 5. F = 11.51 N
  6. 6. y = 0.4221 mm

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