The phenomenon of photoelectric emission occurs only when incident light has:
A. Any frequency if intensity is high
B. Frequency above threshold
C. Long wavelength
D. High intensity
Answer: Option B
Solution (By JKExamLibrary)
Photoelectric effect requires photon energy hν ≥ work function φ of metal. Thus frequency ν must exceed threshold ν₀ = φ/h, regardless of intensity. Intensity affects number of electrons, not emission possibility. Memory aid: 'Photoelectric: frequency threshold (quantum effect); intensity affects current, not emission'. This quantum physics concept is frequently tested in competitive exams. Always distinguish classical wave prediction (intensity-dependent) from quantum reality (frequency-dependent); this was key evidence for photons.
Explanation:
Generator converts mechanical energy (rotation) to electrical energy via electromagnetic induction. Motor does the reverse (electrical to mechanical). Transformer changes AC voltage levels; galvanometer detects small currents. Memory aid: 'Generator: motion ⇒ electricity; Motor: electricity ⇒ motion'. This principle-based question tests understanding of energy conversion devices, crucial for electromagnetism in competitive exams. Always link device function to underlying physics law: generator (Faraday's law), motor (Lorentz force).
Explanation:
Position-time graph as parabola: x = x₀ + ut + ½at². This quadratic form indicates constant acceleration 'a'. If acceleration were changing, the graph would be cubic or higher order. Constant velocity would produce a straight line (linear graph). Upward opening parabola implies positive acceleration. Graph interpretation skill is essential: slope of x-t graph = velocity; curvature indicates acceleration. Memory tip: Parabolic x-t graph ⇔ constant acceleration; linear x-t graph ⇔ constant velocity. Competitive exams frequently test graph-concept correlations.
Explanation:
Convex mirror diverges light, forms virtual, erect, diminished image behind mirror for any object position. Focal length positive by sign convention but image always virtual (upright). Used in rear-view mirrors.
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