The direction of the magnetic field lines around a straight current-carrying conductor can be determined by:
A. Fleming's Right-Hand Rule
B. Faraday's Law
C. Fleming's Left-Hand Rule
D. Right-Hand Thumb Rule
Answer: Option D
Solution (By JKExamLibrary)
Maxwell's Right-Hand Thumb Rule states that if you imagine holding a straight current-carrying conductor in your right hand such that the thumb points in the direction of the current, then the direction in which your fingers wrap around the conductor represents the direction of the circular magnetic field lines.
Explanation:
For spherical mirrors (concave or convex), focal length f = R/2, where R is radius of curvature. This holds under paraxial approximation (small angles). Derivation uses geometry of reflection and small-angle approximations. Memory tip: 'Mirror: f = R/2; Lens: 1/f = (n-1)(1/R₁ - 1/R₂)'. This fundamental relation is frequently tested in optics sections of competitive exams. Always note sign conventions: f negative for convex mirrors, positive for concave; R follows same sign as f.
Explanation:
ΔL = L₀αΔT = 1×2×10⁻⁵×50 = 100×10⁻⁵ = 10⁻³ m = 1 mm. Direct expansion formula application. Memory tip: 'ΔL = LαΔT; convert result to required units'. Tests thermal expansion calculation with unit conversion, frequently appearing in competitive exams.
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