Scientific Instruments — Set 1

Correct Answer: A. Fathometer

• **Fathometer** = A fathometer measures water depth by emitting a sound pulse downward and timing its echo from the ocean floor. • **echo sounding** — It operates on the principle of echo sounding (SONAR); depth = (speed of sound in water × time) ÷ 2, with sound travelling ~1,500 m/s in seawater. • 💡 Wrong-option analysis: Hydrometer: measures density of liquids, not depth; Fluxmeter: measures magnetic flux; Manometer: measures gas or liquid pressure.

Correct Answer: A. Measuring humidity in the air

• **Measuring humidity in the air** = A hygrometer measures the amount of water vapour (relative humidity) in the atmosphere. • **relative humidity** — It provides readings as a percentage; 100% RH means air is fully saturated with water vapour, critical for weather forecasting. • 💡 Wrong-option analysis: Measuring wind speed: that is done by an anemometer; Measuring liquid density: that is done by a hydrometer; Measuring atmospheric pressure: that is done by a barometer.

Correct Answer: C. Milk

• **Milk** = A lactometer measures the specific gravity of milk to detect adulteration with water and check cream content. • **Archimedes' principle** — It works on buoyancy; pure milk has a specific gravity of about 1.026–1.032, and added water reduces this value. • 💡 Wrong-option analysis: Water: purity of water is tested by nephelometer or TDS meter; Oil: oil purity uses different refractometric methods; Honey: honey purity is tested by a refractometer.

Correct Answer: A. Pyrheliometer

• **Pyrheliometer** = A pyrheliometer measures the direct beam solar irradiance reaching Earth's surface, mounted on a solar tracker. • **~1,361 W/m²** — The solar constant at the top of the atmosphere is approximately 1,361 W/m²; pyrheliometer data is vital for solar energy research and climate science. • 💡 Wrong-option analysis: Anemometer: measures wind speed; Chronometer: measures precise time; Galvanometer: measures small electric currents.

Correct Answer: C. Navigation

• **Navigation** = A sextant measures the angle between a celestial body (sun or star) and the horizon to determine a ship's latitude and longitude at sea. • **60-degree arc** = Its name comes from its arc, which spans 1/6 of a circle (60°); navigators use it with astronomical tables to fix their position without GPS. • 💡 Wrong-option analysis: Microbiology: uses microscopes, not sextants; Acoustics: deals with sound, uses sound meters; Geology: uses seismographs and rock hammers.

Correct Answer: C. Seismograph

• **Seismograph** = A seismograph detects and records seismic waves from earthquakes, producing a paper or digital record called a seismogram. • **P-waves and S-waves** — It can detect both primary (P) and secondary (S) waves; the time difference between them helps locate the earthquake's epicentre. • 💡 Wrong-option analysis: Phonograph: records and plays back sound; Spectrograph: records the spectrum of light or sound; Oscillograph: records electrical oscillations on a screen.

Correct Answer: A. Anemometer

• **Anemometer** = An anemometer is the standard meteorological instrument for measuring wind velocity; the cup anemometer spins faster as wind speed increases. • **Beaufort scale** — Wind speed data from anemometers is used to assign Beaufort scale values and generate weather forecasts for aviation and shipping. • 💡 Wrong-option analysis: Hygrometer: measures atmospheric humidity; Altometer: not a standard term (altimeter measures altitude); Barometer: measures atmospheric pressure.

Correct Answer: D. Dynamo

• **Dynamo** = A dynamo (DC generator) converts mechanical energy into electrical energy by rotating an armature within a magnetic field using electromagnetic induction. • **Faraday's principle** — It operates on Faraday's law of electromagnetic induction (1831); before alternators, dynamos were the primary industrial power source. • 💡 Wrong-option analysis: Rectifier: converts AC to DC, does not generate electricity; Transformer: transfers electrical energy between circuits at different voltages; Motor: converts electrical energy into mechanical energy (opposite of dynamo).

Correct Answer: A. Blood pressure

• **Blood pressure** = A sphygmomanometer consists of an inflatable cuff and a pressure gauge to measure arterial blood pressure in mmHg. • **120/80 mmHg** — Normal blood pressure is about 120/80 mmHg (systolic/diastolic); it is used together with a stethoscope to detect Korotkoff sounds. • 💡 Wrong-option analysis: Body temperature: measured by a clinical thermometer; Heart rate: measured by a pulse oximeter or ECG; Lung capacity: measured by a spirometer.

Correct Answer: A. Terrestrial Telescope

• **Terrestrial Telescope** = A terrestrial telescope provides an erect (upright) image of distant objects on the ground, unlike an astronomical telescope which inverts the image. • **erecting lens** — It contains an additional erecting lens system; it is used in bird-watching, land surveillance, and military rangefinding. • 💡 Wrong-option analysis: Periscope: used to see over obstacles using mirrors, not for distant ground objects; Stroboscope: used to study rotating or vibrating objects; Microscope: magnifies tiny nearby objects, not distant ones.