The phenomenon of electromagnetic induction was discovered by:
A. Nikola Tesla
B. Thomas Edison
C. Michael Faraday
D. Heinrich Hertz
Answer: Option C
Solution (By JKSSB Mock Tests)
Michael Faraday discovered electromagnetic induction in 1831. He demonstrated that a changing magnetic field could induce an electric current in a nearby circuit. This groundbreaking discovery laid the foundation for all modern electric generators and transformers. Tesla contributed to AC systems, Edison to DC systems, and Hertz proved the existence of radio waves.
Explanation:
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:
7.50 has three significant figures (7,5,0). Trailing zero after decimal is significant. If it were 7.5 cm, two significant figures. Precision indicated by decimal places.
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