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
−−10 µC++10 µCr = 2 cm

Two point charges of −10 µC and +10 µC are 2 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

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

Point charges of +4 µC and +6 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 = +4 µCq2 = +6 µCF = 2 N
r = cm
3.Medium
++1 µC++4 µCE = 020 cm

Charges of +1 µC and +4 µC are 20 cm apart. At what distance x from the +1 µC charge, on the line between them, is the electric field zero?

q1 = +1 µCq2 = +4 µCd = 20 cm
x = cm
4.Medium
−−6 µC−−4 µCr = 25 cm

Two identical small metal spheres carry charges of −6 µC and −4 µC. They are touched together and then put back 25 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −6 µCq2 = −4 µCr = 25 cm
F = N
5.Hard
+ + + + + +− − − − − −e⁻3 × 10⁷ m/s5 cmE = 4300 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 3 × 10⁷ m/s. The plates are 5 cm long and the field between them is 4300 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 = 5 cmE = 4300 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm
6.Hard
3 cm10 cm+q1​ = +1 µC+q3​ = +6 µC+q2​ = +6 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 6 µC is at the right-angle corner, q₁ = 1 µC is 3 cm from it along one side and q₂ = 6 µC is 10 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 1 µCq2 = 6 µCq3 = 6 µCr13 = 3 cmr23 = 10 cm
F = N

Answer key

  1. 1. F = 2248 N
  2. 2. r = 32.85 cm
  3. 3. x = 6.667 cm
  4. 4. F = 3.596 N
  5. 5. y = 1.05 mm
  6. 6. F = 68.11 N

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