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
++50 nCPr = 15 cm

Find the magnitude of the electric field E at a distance of 15 cm from a point charge of +50 nC. Use k = 8.99 × 10⁹ N·m²/C².

q = +50 nCr = 15 cm
E = N/C
2.Easy
−−10 µCPr = 30 cm

Find the magnitude of the electric field E at a distance of 30 cm from a point charge of −10 µC. Use k = 8.99 × 10⁹ N·m²/C².

q = −10 µCr = 30 cm
E = N/C
3.Medium
++3 µC−−10 µCP40 cm

A charge of +3 µC and a charge of −10 µC are 40 cm apart. Point P lies on the line between them, 24 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +3 µCq2 = −10 µCr1 = 24 cmr2 = 16 cm
E = N/C
4.Medium
−−2 µC++6 µC−−5 µC30 cm + 10 cm

Three point charges lie on a straight line: −2 µC on the left, −5 µC on the right 40 cm away, and +6 µC between them, 30 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 = −2 µCqR = −5 µCqM = +6 µCrL = 30 cmrR = 10 cm
F = N
5.Hard
++P2 × 10 cm4 cm+8 µC+8 µC

Charges of +8 µC and +8 µC are 20 cm apart. Point P lies 4 cm from the midpoint between them, on the perpendicular bisector. Find the magnitude of the electric field E at P. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +8 µCq2 = +8 µCd = 20 cmh = 4 cm
E = N/C
6.Hard
+ + + + + +− − − − − −e⁻2.5 × 10⁷ m/s3 cmE = 2800 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 2.5 × 10⁷ m/s. The plates are 3 cm long and the field between them is 2800 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 = 2.5 × 10⁷ m/sL = 3 cmE = 2800 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. E = 19978 N/C
  2. 2. E = 998889 N/C
  3. 3. E = 3.98 × 10⁶ N/C
  4. 4. F = 25.77 N
  5. 5. E = 4.605 × 10⁶ N/C
  6. 6. y = 0.3546 mm

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