Charges floating in 3D with their field lines traced live. With two charges, change q and r and watch the equal-and-opposite forces follow F = kq₁q₂/r²: double r and the force drops to a quarter. With three, drag the charges around and see the two forces on one of them add, parallelogram and all, to the net force, with every component in a table. Every practice-question arrangement is one click away.
3D ApparatusF = 0.337 N
Loading the 3D apparatus…
drag the space to rotate · grid squares are 5 cm
Positive chargeNegative chargeForce on each charge
The forces on the two charges are always equal in size and opposite in direction (Newton’s third law). Arrows are drawn beside the charges so they never overlap. Field lines run from + to −; arrowheads show the direction of the field.
Charge unit
+2.00 µC
−3.00 µC
0.400 m
Change one thing and watch the force:
Field lines
From the practice questions
Readouts
Force on each charge
0.337 N
The charges…
attract
F = (9.0 × 10⁹ × 2.0 × 10⁻⁶ × 3.0 × 10⁻⁶) ÷ 0.400² = 0.337 N
How the force falls off with distance
Each time r doubles, F falls to a quarter.
F = k q₁ q₂ / r²
k = 9.0 × 10⁹ N·m²/C² · 1 µC = 1 × 10⁻⁶ C
Try This
→Press “Double r”: the force drops to a quarter. That is the inverse-square law.
→Make q₁ much bigger than q₂: the two force arrows stay exactly the same length. Why?
→Flip the sign of one charge: the size of the force stays the same, only its direction changes.
What Each Variable Means
F
Force
The electrostatic force between two charges, in newtons (N). Like charges repel; unlike charges attract.
q
Charge
In coulombs (C). Questions often use µC (× 10⁻⁶), nC (× 10⁻⁹) or mC (× 10⁻³): convert first.
r
Separation
Distance between the centres of the two charges, in metres (m). The force depends on 1/r².
k
Coulomb constant
9.0 × 10⁹ N·m²/C². It sets how strong the electric force is.
