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 = 25 cm

Two point charges of −4 µC and +6 µC are 25 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 = 25 cm
F = N
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 28 N. The first charge is doubled and the distance between the charges is halved. Find the new force F′.

F = 28 Nq₁′ = 2·q₁r′ = 0.5·r
F′ = N
3.Medium
++5 µC++10 µCP50 cm

A charge of +5 µC and a charge of +10 µC are 50 cm apart. Point P lies on the line between them, 30 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +5 µCq2 = +10 µCr1 = 30 cmr2 = 20 cm
E = N/C
4.Medium
++3 µC−−8 µCr = 15 cm

Two identical small metal spheres carry charges of +3 µC and −8 µC. They are touched together and then put back 15 cm apart. Find the magnitude of the force F between them now. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +3 µCq2 = −8 µCr = 15 cm
F = N
5.Hard
+−P2 × 5 cm10 cm+3 µC−3 µC

Charges of +3 µC and −3 µC are 10 cm apart. Point P lies 10 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 = +3 µCq2 = −3 µCd = 10 cmh = 10 cm
E = N/C
6.Hard
+ + + + + +− − − − − −e⁻3.5 × 10⁷ m/s8 cmE = 800 N/C

An electron enters the uniform field between two parallel plates moving parallel to them at 3.5 × 10⁷ m/s. The plates are 8 cm long and the field between them is 800 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 = 3.5 × 10⁷ m/sL = 8 cmE = 800 N/Ce = 1.602 × 10⁻¹⁹ Cme = 9.109 × 10⁻³¹ kg
y = mm

Answer key

  1. 1. F = 3.452 N
  2. 2. F′ = 224 N
  3. 3. E = 1.748 × 10⁶ N/C
  4. 4. F = 2.497 N
  5. 5. E = 1.93 × 10⁶ N/C
  6. 6. y = 0.3675 mm

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