16 public questions tagged with this topic.
Carbon (diamond) has a large energy gap (5.4 eV), preventing electron excitation at room temperature, while Si (1.1 eV) and Ge (0.7 eV) have smaller gaps, allowing thermal excitation and conduction.
Ref: NCERT Physics Textbook for Class XI and XII, Chapter: Relevant Physics topic covering fundamental principles,
Paramagnetic materials lose magnetization when cooled to very low temperatures because thermal energy, which allows weak alignment of atomic moments with an external field, diminishes, leaving the moments randomly oriented in the absence of a field.
Ref: NCERT Physics Textbook - Latest Edition for Academic Session 2026-27 (Rationalized Textbook for Class XI and XII, continuing as per NCERT advisory for 2026-27), Chapter: Kinetic Theory (Latest NCERT 2026-27), Topic: RMS speed v_rms ∝ √T, temperature dependence, ratio v₂/v₁ = √(T₂/T₁) and calculation. The section explains governing laws, formulas like μ₀ = 4π × 10⁻⁷ T·m/A, SI units and illustrative examples. Page.
Elemental semiconductors are pure elements like Si and Ge, while compound semiconductors (e.g., GaAs, CdS) consist of multiple elements. Among the options, Ge is elemental.
Ref: NCERT Physics Textbook for Class XI and XII, Chapter: Relevant Physics topic covering fundamental principles,
Semiconductors have intermediate conductivity ( 10âµ to 10â»â¶ S m^{-1 ), between metals ( 10² to 10⸠S m^{-1 ) and insulators ( 10â»Â¹Â¹ to 10â»Â¹â¹ S m^{-1 ).
Ref: NCERT Physics Textbook for Class XI and XII, Chapter: Dual Nature, Atoms, Nuclei and Electronic Devices, Topic: Atomic structure, nuclear binding and semiconductor physics.
Resistivity ( rho ) distinguishes materials: metals have low resistivity ( 10⁻²to 10⁻⁸Ω m ), semiconductors intermediate ( 10⁻⁵to 10⁶Ω m ), and insulators high ( 10¹⁰to 10¹⁹Ω m ). Among the options, insulators have the highest resistivity.
Ref: NCERT Physics Textbook for Class XI and XII, Chapter: Relevant Physics topic covering fundamental principles,
For a superconductor below its critical temperature, the susceptibility chi = -1 and relative permeability μ_r = 0, but in a broader context, susceptibility can approach zero for non-magnetic materials or when magnetization is negligible compared to the applied field. However, the question implies a specific state, and superconductors achieve this uniquely with perfect diamagnetism.
Ref: NCERT Physics Textbook for Class XI and XII, Chapter: Relevant Physics topic covering fundamental principles,
A positive temperature coefficient ( α ) means resistivity ( rho_t = rho_0 [1 + α (T - T_0)] ) increases with temperature, as increased lattice vibrations reduce the mean free time between collisions, raising resistance.
Ref: NCERT Physics Textbook - Latest Edition for Academic Session 2026-27 (Rationalized Textbook for Class XI and XII, continuing as per NCERT advisory for 2026-27), Chapter: Kinetic Theory (Latest NCERT 2026-27), Topic: RMS speed v_rms ∝ √T, temperature dependence, ratio v₂/v₁ = √(T₂/T₁) and calculation. The section explains governing laws, formulas like μ₀ = 4π × 10⁻⁷ T·m/A, SI units and illustrative examples. Page.
Given: ΔT = 220−20 = 200∘C, ΔA = 0.018cm2, αl = 1.8×10−5K−1. Area expansion: ΔA = A0×2αlΔT. 0.018 = A0×2×1.8×10−5×200. 0.018 = A0×7.2×10−3⇒A0 = 0.0187.2×10−3 = 2.5cm2. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 2.5 cm². This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.
Ref: NCERT Class 11 Physics, Chapter 11: Thermal Properties – Calorimetry.
Given: A0 = 1.2m2, ΔT = 5−45 = −40∘C, αl = 1.2×10−5K−1. Area expansion: ΔA = A0×2αlΔT = 1.2×2×1.2×10−5×(−40). ΔA = 1.2×2.4×10−5×(−40) = −0.001152m2 (decrease of 0.001152m2). As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.001152 m². This satisfies dimensional consistency and physical conditions given, so option D is scientifically correct.
Ref: University Physics, Chapter 17: Thermal Expansion.
