Sound requires material medium for mechanical wave propagation. Vacuum lacks particles to transmit vibrations. Light (EM wave) travels through vacuum. Memory tip: 'Sound = mechanical wave ⇒ needs medium; light = EM wave ⇒ no medium needed'. Fundamental wave property frequently tested in competitive exams to assess medium-dependence understanding.
Explanation:
LED (Light Emitting Diode) emits light when forward biased, due to recombination of electrons and holes. Efficient, long life. Used in displays, lighting. Laser is Light Amplification by Stimulated Emission of Radiation.
Explanation:
Ideal solenoid interior has uniform magnetic field B = μ₀ n I, parallel to axis. Outside field weak. Used in electromagnets, relays. Uniformity for scientific instruments.
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