In short circuit, the value of electric current in a time circuit :

Question

UnlockIAS · Accepted Answer

Correct — C, Increases very high. The whole answer sits in Ohm's law, I = V/R. A short circuit is what happens when the live wire and the neutral wire come into direct contact — through insulation that has cracked or been chewed, a nail driven into a wall, water bridging a socket, or a fault inside the appliance itself. The moment they touch, the current stops flowing through the appliance and takes the new, shorter path instead, so the appliance's resistance drops out of the loop and all that is left is the resistance of the copper wiring, a few hundredths of an ohm. The supply, meanwhile, does not change: the mains is a constant-voltage source pinned at 220 V. With V fixed and R collapsing towards zero, I = V/R has only one way to go, and it goes there steeply. That is precisely how the Commission itself justified this key when it disposed of candidate objections on 31 October 2025 — in a short circuit the resistance becomes close to zero, so by Ohm's law the current rises to a very high value. Put numbers on it. A 100 W bulb on 220 V draws 0.45 A and presents about 484 Ω. Let a fault leave only 0.1 Ω of copper in the loop and Ohm's law demands 220/0.1 = 2,200 A — thousands of times the normal current. And because Joule heating obeys H = I²Rt, the heat released rises with the SQUARE of the current, so a hundredfold current means a ten-thousandfold heating rate. That is why a short circuit melts insulation, welds wires together and starts a fire in seconds, and why the circuit must be broken by a fuse or a miniature circuit breaker within milliseconds. Two notes on the paper itself. The printed English is garbled — 'in a time circuit' is a mis-set rendering of 'at the time of short circuit' — while the Hindi column reads cleanly, which is a standing reason to check the Hindi text of a bilingual BPSC booklet whenever the English reads oddly. And the item is NCERT Class X Science, 'Magnetic Effects of Electric Current' — Chapter 12 with this as Exercise 2 in the book currently in print, Chapter 13 question 5 in older editions, reproduced with all four options in their original sense.

Why the other options are wrong — (a) The exact inverse of what happens, and it is chosen because the word 'short' sounds like 'small'. It refers to the shortened path the current takes, not to a small current. A very low current is the signature of the opposite fault, an OPEN circuit — a broken wire, a blown fuse or an off switch — where the resistance of the path becomes effectively infinite and I = V/R falls to zero. Short circuit and open circuit are the two extreme faults, and they sit at opposite ends of Ohm's law.  (b) This would require the fault to leave the total resistance of the loop untouched, which bridging live and neutral plainly does not. The option is attractive only to a candidate who pictures the mains as pushing a fixed current into the house. It does not: the supply holds the VOLTAGE constant at 220 V, and the current is then whatever Ohm's law demands for the resistance connected across it. Mistaking a voltage source for a current source makes every domestic-circuit question unanswerable.  (d) True of ordinary household current at all times, and therefore a well-designed trap. Indian mains is alternating current at 50 Hz, so it reverses direction 100 times every second whether or not anything has gone wrong — but that is the normal state of the supply, not a description of a fault. The question asks what the MAGNITUDE of the current does when a short occurs: it jumps to a very high value and stays there until the fuse or MCB interrupts the circuit.

Concept: A house is wired as a constant-voltage system. Power arrives on two conductors — the live wire, insulated red, and the neutral wire, insulated black — with 220 V maintained between them in India. A third conductor, the earth wire with green insulation, runs to a metal plate buried deep in the ground near the house; it carries no current in normal use and exists purely as a low-resistance escape path so that if current leaks to the metal body of an iron, toaster or refrigerator, the body stays at earth potential and the user is not shocked. Inside the house the supply is split into separate circuits, typically one rated 5 A for lights and fans and another rated 15 A for geysers and air coolers, and the appliances on each are connected in PARALLEL so that every one of them receives the full 220 V and can be switched independently. Each appliance is, electrically, just a resistance across those 220 V, and how much current it draws is fixed by Ohm's law. Three distinct things can then go wrong, and they are routinely confused. A SHORT CIRCUIT is live meeting neutral directly, so the resistance collapses and the current explodes. An OVERLOAD is too many appliances drawing from one circuit, or an accidental rise in supply voltage, so the current climbs above the wiring's safe rating without any insulation failing. An EARTH LEAKAGE is current escaping to the metal casing of an appliance, which may be far too small to trouble a fuse yet more than enough to kill a person.

State PCS 2025 Q129 — Science & Technology PYQ with Answer

State PCS 2025 Q129 — Science & Technology PYQ with Answer