--- title: "Meissner effect distinguishes type I and II" subject: "Electrical Engineering Material" chapter: 5 key: "semester_3/electrical_engineering_material:meissner-differentiates-types" source: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/meissner-differentiates-types site: BCT Engineering --- # Meissner effect distinguishes type I and II Electrical Engineering Material · Chapter 5: Superconductivity - Asked in: 2076 Chaitra, 4 marks; 2070 Asar, 8 marks (asked 2 times) - Video: [Meissner Effect and Type I & Type II Superconductors by Prof. Manisha Gupta , Lucknow University](https://www.youtube.com/watch?v=dvAy16g75qY) — Physics Department University of Lucknow - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/meissner-differentiates-types - Whole chapter: https://www.bctengineer.com/md/semester_3/electrical_engineering_material/chapter-5 ## Question How does Meissner effect help to differentiate superconductor as type-I and type-II? Explain in brief. ## Short answer Type-I superconductors exhibit complete Meissner effect up to Hc; magnetization -M rises linearly then drops sharply. Type-II superconductors show perfect expulsion only up to Hc1; between Hc1 and Hc2 flux enters as vortices and -M decreases gradually. This magnetization curve distinguishes the two types. ## Answer The Meissner effect (expulsion of flux, $B = 0$ inside, $M = -H$) behaves differently in the two classes of superconductors. Plotting magnetization $-M$ against applied field $H$ separates them clearly. #### Type-I (soft) superconductors - Show a **complete Meissner effect** right up to the critical field $H_c$: $-M$ rises linearly with $H$ (perfect diamagnetism). - At $H = H_c$ the flux enters all at once, $M$ drops sharply to zero and the material becomes normal. - $H_c$ is low (about 0.01 to 0.2 T). Examples: Pb, Hg, Sn, Al. #### Type-II (hard) superconductors - Show a complete Meissner effect only up to the **lower critical field** $H_{c1}$. - Between $H_{c1}$ and $H_{c2}$ flux partly enters as quantized vortices, so the Meissner effect is **incomplete** (mixed or vortex state). $-M$ falls gradually. - At the **upper critical field** $H_{c2}$, $M = 0$ and the material is normal. $H_{c2}$ can be tens of tesla. Examples: NbTi, Nb$_3$Sn, YBCO. ```text -M -M | /| | /\ | / | | / \ | / | | / \_ | / | |/ \__ |/ |____ H +----|------|--- H 0 Hc 0 Hc1 Hc2 Type-I Type-II ``` | Point | Type-I | Type-II | |---|---|---| | Meissner effect | Complete up to $H_c$ | Complete only below $H_{c1}$ | | Change at critical field | Abrupt | Gradual | | Critical fields | One ($H_c$) | Two ($H_{c1}$, $H_{c2}$) | | Mixed state | Absent | Present | So by measuring how $M$ varies with $H$, a sharp drop identifies type-I and a gradual fall over a range identifies type-II. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What happens to -M of a type-I superconductor at H = Hc? A. M drops sharply to zero as flux enters all at once B. -M falls gradually to zero up to Hc2 C. -M stays at its maximum value above Hc D. -M reverses sign slowly Answer: A. Type-I has an abrupt transition at Hc. (Key point: Type-I magnetization curve) 2. Up to which field is the Meissner effect complete in a type-II superconductor? A. Hc2, the upper critical field B. Hc1, the lower critical field C. Hc, a single critical field D. It is never complete Answer: B. Below Hc1 flux is fully expelled; above it vortices enter. (Key point: Type-II Meissner effect) 3. What is true at Hc2 in type-II? A. The Meissner effect becomes complete B. The vortices disappear and perfect diamagnetism returns C. M = 0 and the material is normal D. Resistance becomes zero for the first time Answer: C. At Hc2 vortices overlap and the material becomes normal. (Key point: Upper critical field) 4. How does the M versus H plot identify the type? A. A gradual fall means type-I; a sharp drop means type-II B. Both give identical plots C. Only the slope below Hc decides it D. A sharp drop means type-I; a gradual fall over a range means type-II Answer: D. The manner in which M falls to zero separates the two classes. 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