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
−−2 µC++6 µCr = 20 cm

Two point charges of −2 µC and +6 µC are 20 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = −2 µCq2 = +6 µCr = 20 cm
F = N
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 52 N. The first charge is doubled and the distance between the charges is made four times as large. Find the new force F′.

F = 52 Nq₁′ = 2·q₁r′ = 4·r
F′ = N
3.Medium
++10 µC++1 µCr = 10 cm

Two identical small metal spheres carry charges of +10 µC and +1 µC. They are touched together and then put back 10 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +10 µCq2 = +1 µCr = 10 cm
F = N
4.Medium
++4 µC++1 µCP30 cm

A charge of +4 µC and a charge of +1 µC are 30 cm apart. Point P lies on the line between them, 15 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +4 µCq2 = +1 µCr1 = 15 cmr2 = 15 cm
E = N/C
5.Hard
++P2 × 8 cm6 cm+6 µC+6 µC

Charges of +6 µC and +6 µC are 16 cm apart. Point P lies 6 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 = +6 µCq2 = +6 µCd = 16 cmh = 6 cm
E = N/C
6.Hard
+ + + + + +− − − − − −e⁻2.5 × 10⁷ m/s5 cmE = 900 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 5 cm long and the field between them is 900 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 = 5 cmE = 900 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. F = 2.697 N
  2. 2. F′ = 6.5 N
  3. 3. F = 27.19 N
  4. 4. E = 1.199 × 10⁶ N/C
  5. 5. E = 6.473 × 10⁶ N/C
  6. 6. y = 0.3166 mm

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