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++5 µCr = 30 cm

Two point charges of +4 µC and +5 µC are 30 cm apart. Find the magnitude of the electric force F between them. Use k = 8.99 × 10⁹ N·m²/C².

q1 = +4 µCq2 = +5 µCr = 30 cm
F = N
2.Easy
+q₁+q₂r

Two point charges repel each other with a force of 46 N. The first charge is made four times as large and the distance between the charges is halved. Find the new force F′.

F = 46 Nq₁′ = 4·q₁r′ = 0.5·r
F′ = N
3.Medium
++3 µC−−2 µCP60 cm

A charge of +3 µC and a charge of −2 µC are 60 cm apart. Point P lies on the line between them, 36 cm from the first charge. Find the magnitude of the electric field E at P.

q1 = +3 µCq2 = −2 µCr1 = 36 cmr2 = 24 cm
E = N/C
4.Medium
−−8 µC++10 µC++2 µC8 cm + 12 cm

Three point charges lie on a straight line: −8 µC on the left, +2 µC on the right 20 cm away, and +10 µC between them, 8 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 = −8 µCqR = +2 µCqM = +10 µCrL = 8 cmrR = 12 cm
F = N
5.Hard
++P2 × 8 cm5 cm+6 µC+6 µC

Charges of +6 µC and +6 µC are 16 cm apart. Point P lies 5 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 = 5 cm
E = N/C
6.Hard
3 cm4 cm+q1​ = +2 µC+q3​ = +2 µC+q2​ = +4 µC

Three positive point charges sit at the corners of a right triangle: q₃ = 2 µC is at the right-angle corner, q₁ = 2 µC is 3 cm from it along one side and q₂ = 4 µC is 4 cm from it along the other side. Find the magnitude of the net electric force F on q₃.

q1 = 2 µCq2 = 4 µCq3 = 2 µCr13 = 3 cmr23 = 4 cm
F = N

Answer key

  1. 1. F = 1.998 N
  2. 2. F′ = 736 N
  3. 3. E = 520255 N/C
  4. 4. F = 124.9 N
  5. 5. E = 6.424 × 10⁶ N/C
  6. 6. F = 60.14 N

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