(A) (i) Why is an alternating current (A.C.) considered to be advantageous over direct current (D.C.) for the long distance transmission of electric power ?
(ii) How is the type of current used in household supply different from the one given by a battery of dry cells ?
(iii) How does an electric fuse prevent the electric circuit and the appliances from a possible damage due to short circuiting or overloading.
Generated by claude-sonnet-4-6 · 2026-06-15 06:44 · grounding rag
Model Answer
(i) A.C. voltage can be stepped up using a transformer, which reduces current and hence power loss ($P = I^2R$) during long-distance transmission. D.C. cannot be stepped up/down easily, making it less suitable for long-distance transmission.
(ii) Household supply uses alternating current (A.C.) — the direction of current reverses periodically (50 Hz in India). A battery of dry cells provides direct current (D.C.) — current flows in one fixed direction only.
(iii) A fuse wire has high resistance and a low melting point. During short-circuiting or overloading, excessive current flows, which heats and melts the fuse wire, breaking the circuit. This prevents damage to wiring and appliances.
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Explanation
- Part (i) focuses on the transformer advantage of A.C. — the key phrase is "step up voltage → reduce current → reduce $I^2R$ loss."
- Part (ii) requires the two key terms: A.C. (alternating) for household, D.C. (direct/unidirectional) for battery.
- Part (iii) must mention: high resistance + low melting point of fuse → melts on excess current → breaks circuit. These are the examiner's expected points.