The meter that is used to measure the distance moved by the vehicle is known as

Question

UnlockIAS · Accepted Answer

Correct — C, Odometer. The word is assembled from the Greek hodos, meaning a road or way, and metron, a measure — a road-measurer — and that is precisely its function: it counts the total distance a vehicle has covered and displays it, in India normally in kilometres, on the instrument cluster. The mechanism explains the name. A classical odometer is driven off the transmission or a wheel, and since each full rotation of a wheel carries the vehicle forward by exactly the circumference of its tyre, counting rotations and multiplying by that circumference gives distance. Modern vehicles do the same arithmetic electronically, with a sensor generating pulses that the cluster's processor counts. Two consequences of that design are examinable in their own right. First, fitting tyres of a different size changes the reading, because the calibration assumes a fixed circumference. Second, an odometer measures path length and not displacement — drive twenty kilometres out and twenty back, and your displacement is zero while the odometer has advanced by forty. Most vehicles in fact carry two: a main odometer that cannot normally be reset, which serves as the legal record of how much the vehicle has been used, and a resettable trip meter for measuring a single journey. The other three options are all real instruments in daily use, and each measures something entirely unrelated to distance, which is exactly what this question is checking.

Why the other options are wrong — (a) Speedometer — the instrument that sits immediately next to the odometer on the same cluster, which is why it is the trap. It measures the rate at which distance is being covered rather than the distance itself, and since speed is distance divided by time, the two instruments stand in the relation of a quantity to its rate of change. A driver reads the speedometer to answer 'how fast am I going right now' and the odometer to answer 'how far has this vehicle travelled in all'.  (b) Ammeter — a contraction of ampere-meter, an instrument that measures electric current and is connected in series in a circuit so that the whole current passes through it. It belongs to the electricity chapter of the syllabus and has no connection with motion or distance. It appears on this list only because its name ends in the same suffix as the answer.  (d) Chronometer — from the Greek chronos, time: a precision timekeeper rather than a distance measurer. It is worth remembering for its own sake, because the marine chronometer is what made longitude determinable at sea, a navigator comparing local noon with the time still shown for a reference meridian. That is a distance calculation of a kind, which is what gives the option a faint plausibility, but the instrument itself measures only time.

Concept: Almost every instrument in the school science syllabus announces what it measures in its own name, because the names are built from Greek and Latin roots joined to metron, a measure. Learning the roots converts a long memorisation list into a short one: hodos is a road, so an odometer measures distance travelled; tachys is swift, so a tachometer measures rotational speed in revolutions per minute; chronos is time, baros is weight and hence pressure, hygros is wet and hence humidity, anemos is wind, seismos is a shaking, and sphygmos is the pulse. The standard set an Indian examiner draws from is finite and recurs every year: odometer for distance, speedometer for instantaneous speed, tachometer for engine revolutions, ammeter for current, voltmeter for potential difference, galvanometer for very small currents, barometer for atmospheric pressure, manometer for gas pressure, hygrometer for humidity, anemometer for wind speed, thermometer and pyrometer for ordinary and very high temperatures, hydrometer for the relative density of a liquid, lactometer for the purity of milk, altimeter for altitude, fathometer for ocean depth, seismograph for earthquake waves, audiometer for hearing and sphygmomanometer for blood pressure.

State PCS 2024 Q25 — Science & Technology PYQ with Answer

State PCS 2024 Q25 — Science & Technology PYQ with Answer