The phenomenon of photoelectric emission occurs only when incident light has:
A. Frequency above threshold
B. Long wavelength
C. High intensity
D. Any frequency if intensity is high
Answer: Option A
Solution (By JKSSB Mock Tests)
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:
Spherical mirrors: f = R/2 under paraxial approximation. Derived from geometry of reflection. Memory tip: 'Mirror: f = R/2; sign: concave +, convex -'. Optics formula frequently tested in competitive exams.
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