Work per unit charge to move between points is: MCQ with Answer and Explanation

Explanation:
LED (Light Emitting Diode) works on electroluminescence: when electrons recombine with holes in a semiconductor junction, energy is released as photons. This is distinct from incandescence (heating filament, like bulbs), fluorescence (absorb UV, emit visible), or heating effect. Memory aid: 'LED = semiconductor light emission; no filament'. This modern application question tests knowledge of everyday physics, common in competitive exams. Always link device to underlying phenomenon: LED (electroluminescence), laser (stimulated emission), solar cell (photovoltaic effect).

Explanation:
Newton's Law of Universal Gravitation states that the gravitational force (F) between two point masses is directly proportional to the product of their masses (m1 × m2) and inversely proportional to the square of the distance (r²) between their centers. The mathematical formula is F = G(m1m2)/r².

Explanation:
Nuclear fusion: e.g., hydrogen isotopes deuterium and tritium fuse to helium, releasing energy. Powers Sun and stars. Requires high temperature (thermonuclear). Fusion reactor under development.