Which of the following devices relies on the heating effect of electric current? MCQ with Answer and Explanation

Explanation:
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.

Explanation:
Force = rate of change of momentum: F = Δp/Δt. Thus Δp = F × Δt = 10 N × 5 s = 50 kg·m/s. Since initial momentum was zero (body at rest), final momentum = 50 kg·m/s. Alternatively, acceleration a = F/m = 10/2 = 5 m/s², velocity after 5s: v = u + at = 0 + 5×5 = 25 m/s, momentum p = mv = 2×25 = 50 kg·m/s. Both methods confirm. Memory tip: Impulse (FΔt) equals change in momentum. This direct application of Newton's second law is essential for dynamics problems in competitive exams.

Explanation:
Generator converts mechanical energy (rotation) to electrical energy via electromagnetic induction. Motor does the reverse (electrical to mechanical). Transformer changes AC voltage levels; galvanometer detects small currents. Memory aid: 'Generator: motion ⇒ electricity; Motor: electricity ⇒ motion'. This principle-based question tests understanding of energy conversion devices, crucial for electromagnetism in competitive exams. Always link device function to underlying physics law: generator (Faraday's law), motor (Lorentz force).