Magnetic field around straight current-carrying wire is:
A. Parallel to wire
B. Radial
C. Uniform
D. Circular concentric
Answer: Option D
Solution (By JKSSB Mock Tests)
Biot-Savart law: field forms concentric circles around wire, direction by right-hand thumb rule. Magnitude B = μ₀I/(2πr), decreasing with distance. Memory tip: 'Right-hand rule: thumb = current, fingers = field circles'. Fundamental magnetism concept frequently tested in competitive exams.
Explanation:
At maximum height, final velocity v = 0. Using v = u - gt (taking upward positive), 0 = u - gt ⇒ t = u/g. This is time of ascent. Total time of flight would be 2u/g. The equation derives from Newton's first equation of motion under constant acceleration g downward. Memory aid: Time to peak = initial velocity / gravitational acceleration. This fundamental result appears in projectile motion problems. Competitive exams often combine this with energy conservation or symmetry concepts for advanced questions.
Explanation:
Coefficient of performance (COP) for refrigerator: COP = Q₂ / W, where Q₂ is heat extracted from cold reservoir, W is work input. By energy conservation, Q₁ = Q₂ + W (heat rejected to hot reservoir). COP > 1 typically. Option A is inverse; C and D relate to heat engine efficiency. Memory aid: 'Refrigerator COP = desired output (cooling) / work input'. This thermodynamics definition is frequently tested in competitive exams. Always distinguish refrigerator COP (cooling effect per work) from heat engine efficiency (work output per heat input).
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