Explanation:
Potentiometer uses null method: at balance, no current flows through cell, so measured voltage equals true EMF (no internal resistance drop). Memory aid: 'Null method ⇒ zero current ⇒ accurate EMF measurement'. Experimental physics concept frequently tested in competitive exams to verify understanding of precision measurement techniques.
Explanation:
Solar cell (photovoltaic cell) converts sunlight directly into electricity using semiconductor p-n junction. No heat involved. Battery converts chemical to electrical. Thermocouple heat to electrical. Solar energy is renewable.
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