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#perfect conductor

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Torque on Magnetic Dipole and Potential Energy

A material that conducts electricity perfectly and repels magnetic fields is likely operating as:

**Torque on magnetic dipole** in uniform field B is τ = m × B, magnitude τ = m B sinθ, m moment (A·m²), B field (T), θ angle between m and B (degrees). Torque tends to align moment with field, zero at θ = 0°, maximum mB at 90°, direction given by right-hand rule. Superconductors, when below their critical temperature, exhibit zero electrical resistance (perfect conductivity) and perfect diamagnetism (repelling magnetic fields via the Meissner effect), a unique combination not seen in other materials. Substituting values gives A superconductor, which matches expected magnitude for this magnetic configuration, confirming dipole field dependence on m/r³ and torque

Ref: NCERT > Physics Book > Magnetism and Matter > Torque on Magnetic Dipole and Potential Energy

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Torque on Magnetic Dipole and Potential Energy

A material that conducts electricity perfectly while expelling magnetic fields relies on:

**Magnetic dipole in uniform field** experiences torque τ = m B sinθ and potential energy U = -m·B = -m B cosθ, minimum -mB when aligned (θ=0°), maximum +mB at anti-alignment (θ=180°). Work done rotating from θ₁ to θ₂ equals ΔU = mB(cosθ₁ - cosθ₂). Superconductors achieve perfect conductivity and expel magnetic fields (Meissner effect) below their critical temperature, where induced surface currents counteract the external field, a phenomenon tied to zero resistance and perfect diamagnetism. Substituting values gives Induced surface currents, which matches expected magnitude for this magnetic configuration, confirming dipole field dependence on m/r³ and torque relation τ = m B sinθ.

Ref: NCERT > Physics Book > Magnetism and Matter > Torque on Magnetic Dipole and Potential Energy

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