Scientific Instruments — Set 2

Correct Answer: C. Very high temperatures

• **Very high temperatures** = A pyrometer is a non-contact thermometer that measures very high surface temperatures by detecting thermal radiation emitted by the object. • **600°C and above** — Pyrometers are accurate for temperatures above ~600°C and are essential for monitoring molten metals in steel furnaces and kilns. • 💡 Wrong-option analysis: Light intensity: measured by a photometer or lux meter; Very low temperatures: measured by a cryometer; Atmospheric pressure: measured by a barometer.

Correct Answer: B. Auxanometer

• **Auxanometer** = An auxanometer measures the increase in length or volume of plant organs over time, using a pulley and pointer system to magnify small increments. • **J.C. Bose** = Sir J.C. Bose invented the high-precision crescograph for similar plant growth measurements, demonstrating plant sensitivity to stimuli. • 💡 Wrong-option analysis: Hydrometer: measures liquid density; Spherometer: measures curvature of spherical surfaces; Odometer: measures distance travelled by a vehicle.

Correct Answer: D. Galvanometer

• **Galvanometer** = A galvanometer is a highly sensitive instrument that detects and measures very small electric currents by deflecting a needle in a magnetic field. • **bridge circuits** — It is used in Wheatstone bridge circuits for precise resistance measurements and can be converted into an ammeter or voltmeter by adding resistors. • 💡 Wrong-option analysis: Wattmeter: measures electric power in watts; Ammeter: measures larger currents (milliamperes and above); Voltmeter: measures potential difference in volts.

Correct Answer: A. Altimeter

• **Altimeter** = An altimeter determines the height of an aircraft above a reference level (usually sea level) by measuring atmospheric pressure, which decreases with altitude. • **barometric principle** — A barometric altimeter uses the fact that air pressure drops by ~1 hPa for every 8 m of altitude gained; radar altimeters are also used for ground clearance. • 💡 Wrong-option analysis: Audiometer: evaluates hearing sensitivity; Anemometer: measures wind speed; Binoculars: optical instruments for viewing distant objects, not altitude measurement.

Correct Answer: D. To see objects above sea level from a submarine

• **To see objects above sea level from a submarine** = A periscope uses two mirrors (or prisms) set at 45° to allow a submerged submarine crew to observe the surface without surfacing. • **reflection** — It works on the principle of reflection of light; the simplest design uses two plane mirrors arranged parallel to each other at 45° angles. • 💡 Wrong-option analysis: To magnify small objects: that is the function of a microscope; To see objects inside a liquid: that is done with an underwater camera or endoscope; To measure the speed of light: done using Fizeau's or Michelson's apparatus.

Correct Answer: D. Karatmeter

• **Karatmeter** = A karatmeter uses X-ray fluorescence (XRF) technology to non-destructively determine the purity of gold in carats or percentage. • **24 carats = 100% gold** — Pure gold is 24 carats; a karatmeter gives results in seconds without damaging the jewellery, making it standard in gold shops. • 💡 Wrong-option analysis: Lactometer: measures specific gravity of milk to check purity; Sonometer: studies vibration frequency of strings; Hydrometer: measures liquid density.

Correct Answer: D. Precise time

• **Precise time** = A chronometer is a highly accurate timepiece designed to maintain precision even under changing temperatures, pressure, and ship motion. • **John Harrison** — John Harrison invented the first practical marine chronometer (H4) in 1759, solving the longitude problem for navigation at sea. • 💡 Wrong-option analysis: Magnetic field: measured by a magnetometer; Water pressure: measured by a manometer or pressure gauge; Color intensity: measured by a colorimeter or spectrophotometer.

Correct Answer: B. Spherometer

• **Spherometer** = A spherometer uses a central screw and three fixed legs to measure the radius of curvature of spherical surfaces such as lenses and mirrors. • **R = (l²/6h) + h/2** — The radius of curvature R is calculated using the formula involving the leg distance l and the sagitta h measured by the central screw. • 💡 Wrong-option analysis: Micrometer (screw gauge): measures small thickness or diameter, not curvature; Spectrometer: measures wavelengths of light; Viscometer: measures viscosity of liquids.

Correct Answer: B. Audiometer

• **Audiometer** = An audiometer evaluates a person's hearing sensitivity by generating tones at various frequencies and intensities; results are plotted as an audiogram. • **decibels (dB)** — Hearing threshold is measured in decibels (dB); normal hearing range is 0–25 dB; audiometers are standard tools in ENT clinics. • 💡 Wrong-option analysis: Eudiometer: measures the volume of gases in chemical reactions; Photometer: measures light intensity; Sonometer: studies the relationship between frequency and string tension, not sound intensity.

Correct Answer: B. Hydrophone

• **Hydrophone** = A hydrophone is an underwater microphone that converts acoustic (sound) energy into electrical signals for recording or analysis. • **marine biology and sonar** — Hydrophones are used to study whale calls, detect submarine activity, and monitor underwater earthquakes; sound travels ~4.4× faster in water than in air. • 💡 Wrong-option analysis: Gramophone: plays pre-recorded sound using a needle on a disc; Dictaphone: records spoken words for transcription; Microphone: converts air-borne sound to electrical signals, not designed for underwater use.