| Application | Principle Used | Key Physics |
|---|---|---|
| MRI (Magnetic Resonance Imaging) | Superconducting solenoid creates B ≈ 1.5–3 T; proton spins align | B = μ_{0}nI; extremely high n with superconducting coils; uniform field in bore |
| Electric Motor | Torque on current-carrying loop in magnetic field | τ = NIAB sinθ; torque drives rotation; commutator reverses current direction |
| Loudspeaker | Force on current in a radial magnetic field | F = BIl; varying audio current → varying force → cone vibration → sound |
| Cyclotron | Charged particle in uniform B traces semicircles of increasing radius | f = — cyclotron frequency is velocity-independent; particle accelerated at each gap |
| Magnetic Hard Drive | Ferromagnetic domains aligned to store bits (0 or 1) | High coercivity hard ferromagnet; read head detects stray field of domains |
| Magnetic Compass | Earth's magnetic field exerts torque on needle (ferromagnetic) | τ = MB sinθ; needle aligns to minimise potential energy (θ → 0) |
| Electromagnet | Soft iron core inside solenoid; B = μᵣμ_{0}nI ≈ μᵣ × (air field) | Soft ferromagnet (low coercivity) — easily switched; μᵣ up to 10^{5} gives huge amplification |
| Transformer Core | Alternating flux in soft iron laminate core | Soft iron: low hysteresis loss (small loop area); lamination reduces eddy currents |
NEET relevance: The MRI and cyclotron are frequently mentioned in conceptual questions. The cyclotron's key feature is that its frequency f = does NOT depend on particle speed — this is the same principle as T = 2π being velocity-independent.