A wire of length L and resistance R is stretched so that its length becomes 3L. New resistance is MCQ with Answer and Explanation

Explanation:
Silicon semiconductor, abundant, efficient for photovoltaic cells. Also gallium arsenide. Solar cells convert light to electricity. Renewable energy technology.

Explanation:
Atomic diameter ~ 1 Å = 10⁻¹⁰ m. Nucleus is 10⁻¹⁵ m (femtometre). Atomic size determined by electron cloud. 10⁻⁶ m is typical cell size. 10⁻³ m is millimetre.

Explanation:
Carnot efficiency η = 1 - T₂/T₁, where T₁ is source temperature, T₂ sink temperature (in Kelvin). Here T₁=400 K, T₂=300 K, so η = 1 - 300/400 = 1 - 0.75 = 0.25 = 25%. This maximum possible efficiency for given temperatures is a fundamental thermodynamics result. Memory tip: 'η_Carnot = 1 - T_cold/T_hot'. Competitive exams frequently test this formula with varying temperatures. Always use absolute temperatures (Kelvin); Celsius would yield incorrect efficiency. This problem assesses understanding of heat engine limitations.