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The magnetic effects of electric current form a crucial 3%-weightage topic in JEE, connecting the behavior of moving charges to the magnetic fields they produce. Unlike electrostatics where charges create radial fields, currents create fields that curl around conductors — magnetic field lines always form closed loops, reflecting the absence of magnetic monopoles.

Two complementary laws govern magnetic field calculations: the Biot-Savart law provides the field from arbitrary current geometries through direct integration ($d\vec{B} = \frac{\mu_0}{4\pi}\frac{Id\vec{l} \times \hat{r}}{r^2}$), while Ampere's circuital law ($\oint \vec{B} \cdot d\vec{l} = \mu_0 I_{\text{enc}}$) elegantly handles symmetric distributions like infinite wires, solenoids, and toroids. The choice between them is a key problem-solving skill.

Force interactions between current-carrying conductors ($F = BIL\sin\theta$, force between parallel wires $F/l = \mu_0 I_1 I_2/(2\pi d)$), torque on current loops ($\tau = NIAB\sin\theta$), and the moving coil galvanometer complete the chapter. JEE problems frequently test composite wire shapes (arcs + straight segments), field superposition, and the distinction between solenoid and toroid configurations. Mastery requires fluent application of the right-hand rule and careful attention to geometry.