The coefficient of performance of a refrigerator is defined as:
A. Heat rejected / Work input
B. Work input / Heat extracted
C. Work input / Heat rejected
D. Heat extracted / Work input
Answer: Option D
Solution (By JKSSB Mock Tests)
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).
Explanation:
Acceleration a = dv/dt ⇒ dv = a·dt. Integrating: ∫dv = ∫a·dt ⇒ Δv = area under a-t graph. Slope of v-t gives acceleration; area under a-t gives velocity change. Memory aid: 'a-t graph area = Δv; v-t graph area = displacement'. Graph interpretation skill essential for motion analysis in competitive exams.
A ray of light traveling from water (denser) into air (rarer) grazes the interface separating the two media. The angle of incidence in the water is called the:
Explanation:
When light travels from an optically denser medium to a rarer medium, it bends away from the normal. As the angle of incidence increases, the angle of refraction also increases. The specific angle of incidence for which the refracted ray grazes the surface (meaning the angle of refraction is exactly 90 degrees) is defined as the critical angle.
No comments yet. Be the first to start the discussion!