Solar cells (photovoltaic cells) convert light energy (photons) directly into electrical energy via the photovoltaic effect: photons excite electrons in semiconductor material, creating electron-hole pairs that generate voltage. This is distinct from solar thermal (light to heat to electricity) or batteries (chemical to electrical). Memory aid: 'Photo = light; voltaic = electricity'. This renewable energy application question tests knowledge of energy conversion principles, common in competitive exams. Always distinguish photovoltaic (direct light-electricity) from other solar technologies.
A ray of light traveling from water (denser) into air (rarer) grazes the interface separating the two media. The angle of incidence in the water is called the:
Explanation:
When light travels from an optically denser medium to a rarer medium, it bends away from the normal. As the angle of incidence increases, the angle of refraction also increases. The specific angle of incidence for which the refracted ray grazes the surface (meaning the angle of refraction is exactly 90 degrees) is defined as the critical angle.
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