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 = 12 cm

Two point charges of −10 µC and +10 µC are 12 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 = 12 cm
F = N
2.Easy
+ + + + + +− − − − − −e⁻E = 4600 N/C

A proton (charge 1.602 × 10⁻¹⁹ C, mass 1.673 × 10⁻²⁷ kg) is in a uniform electric field of 4600 N/C. Ignoring gravity, find the magnitude of its acceleration a.

E = 4600 N/C|q| = 1.602 × 10⁻¹⁹ Cm = 1.673 × 10⁻²⁷ kg
a = m/s²
3.Medium
++3 µC−−10 µCr = 40 cm

Two identical small metal spheres carry charges of +3 µC and −10 µC. They are touched together and then put back 40 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = −10 µCr = 40 cm
F = N
4.Medium
++8 µC−−5 µCP20 cm

A charge of +8 µC and a charge of −5 µC are 20 cm apart. Point P lies on the line between them, 8 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +8 µCq2 = −5 µCr1 = 8 cmr2 = 12 cm
E = N/C
5.Hard
10 cm4 cm+q1​ = +5 µC+q3​ = +8 µC+q2​ = +8 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 8 µC is at the right-angle corner, q₁ = 5 µC is 10 cm from it along one side and q₂ = 8 µC is 4 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 5 µCq2 = 8 µCq3 = 8 µCr13 = 10 cmr23 = 4 cm
F = N
6.Hard
+ + + + + +− − − − − −e⁻1.5 × 10⁷ m/s6 cmE = 2700 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 1.5 × 10⁷ m/s. The plates are 6 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 = 1.5 × 10⁷ m/sL = 6 cmE = 2700 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. F = 62.43 N
  2. 2. a = 4.405 × 10¹¹ m/s²
  3. 3. F = 0.6883 N
  4. 4. E = 1.436 × 10⁷ N/C
  5. 5. F = 361.4 N
  6. 6. y = 3.799 mm

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