Electrician / Lineman — 2025 — Official Paper — Kerala PSC PYQ Practice with Answers

Correct answer (Option C):\n\nThe resistance of a conductor is determined by the law of resistance formula:\nFormula: R = ρ × (L / A)\n\nWhere:\nρ = Resistivity of the material\nL = Length of the wire\nA = Cross-sectional area\n\nFrom this expression, resistance (R) is directly proportional to the length (L) of the wire. Therefore, as the length of the wire increases, the resistance to the flow of current increases proportionally.\n\nOption C is correct.\n\nWhy others are wrong:\nOption A and Option B are incorrect because an increase in diameter increases the cross-sectional area (A = πd²/4). Since resistance is inversely proportional to the area, increasing the diameter decreases the resistance.\nOption D is incorrect because resistance increases with length rather than decreasing.\n\nStudy tip:\nAlways remember that longer wires offer more opposition to current flow, while thicker wires with larger cross-sectional areas provide a wider path, lowering the overall resistance.

Correct answer (Option B):\n\nSilver possesses the lowest electrical resistivity among all elements at room temperature, approximately 1.59 × 10⁻⁸ Ω·m. Electrical resistivity measures how strongly a material opposes the flow of electric current. Because silver offers the least resistance, it is considered the best electrical conductor.\n\nOption B is correct.\n\nWhy others are wrong:\nOption A is incorrect because copper has a slightly higher resistivity than silver (approx 1.68 × 10⁻⁸ Ω·m), making it the second best conductor.\nOption C is incorrect because carbon is a non-metal semiconductor with significantly higher resistivity.\nOption D is incorrect because tungsten is a metal used for lamp filaments due to its high melting point and higher resistivity compared to silver and copper.\n\nStudy tip:\nAlthough silver is the best conductor with the lowest resistivity, copper and aluminium are preferred in commercial wiring applications due to their cost-efficiency and abundance.

Correct answer (Option D):\n\nThe temperature coefficient of resistance (α) is defined as the change in electrical resistance of a material per ohm of its initial resistance per degree change in temperature. For pure metals, this coefficient is positive, meaning their resistance increases as temperature goes up.\n\nOption D is correct.\n\nWhy others are wrong:\nOption A is incomplete because it ignores the initial baseline resistance.\nOption B is incorrect because it describes a decrease, which applies to materials with a negative temperature coefficient, whereas conductors have a positive coefficient.\nOption C is grammatically incomplete and lacks the explicit mention of the fractional change per degree.\n\nStudy tip:\nPure metallic conductors like copper, aluminum, and silver always exhibit a positive temperature coefficient of resistance, whereas semiconductors and insulators have a negative temperature coefficient.

Correct answer (Option A):\n\nOhm's Law states that the current (I) flowing through a conductor is directly proportional to the potential difference (V) across its ends, provided physical conditions remain constant.\nFormula: V = I × R\n\nWhen plotting voltage on the y-axis and current on the x-axis, the relationship yields a straight line passing through the origin. The slope of this line represents the constant resistance (R), making the graph strictly linear.\n\nOption A is correct.\n\nWhy others are wrong:\nOption B is incorrect because a parabola represents a quadratic relationship, such as power loss vs current (P = I²R).\nOption C is incorrect because a hyperbola indicates an inverse relationship.\nOption D is incorrect because a sine function represents alternating current waveforms over time, not the static V-I relationship.\n\nStudy tip:\nMaterials that follow this linear V-I relationship are called ohmic conductors. Linear components maintain a stable resistance across varying voltage thresholds.

Correct answer (Option C):\n\nInsulators are materials that heavily oppose the movement of electric charges because their valence electrons are tightly bound to their parent atoms. This results in an extremely high electrical resistivity. Since electrical conductivity is the mathematical inverse of resistivity, the conductivity of insulators is exceptionally low, practically approaching zero.\n\nOption C is correct.\n\nWhy others are wrong:\nOption A is incorrect because high conductivity is a characteristic property of good conductors like silver and copper.\nOption B is incorrect because medium conductivity describes semiconductors like silicon and germanium.\nOption D is incorrect because "positive" describes a mathematical sign rather than a scale of magnitude for material conduction limits.\n\nStudy tip:\nCommon industrial electrical insulators include glass, mica, quartz, porcelain, and dry rubber, all of which feature negligible free electron availability.