Scientific Instruments — Set 5

Correct Answer: A. Determining orientation and angular velocity

• **Determining orientation and angular velocity** = A gyroscope uses a rapidly spinning wheel to maintain a fixed orientation in space, enabling measurement of angular velocity and direction. • **conservation of angular momentum** — Its stability is due to conservation of angular momentum; used in aircraft autopilots, ship navigation, and smartphone orientation sensors. • 💡 Wrong-option analysis: Measuring gravity: done by a gravimeter or pendulum apparatus; Measuring light intensity: done by a photometer; Checking liquid density: done by a hydrometer.

Correct Answer: B. Manometer

• **Manometer** = A manometer measures the pressure of gas or liquid inside a closed container by comparing it against a reference pressure using a liquid column. • **U-tube design** — A simple U-tube manometer uses a liquid column height to indicate pressure difference; widely used in laboratories and industrial gas pipelines. • 💡 Wrong-option analysis: Barometer: measures atmospheric (outdoor) pressure, not enclosed gas pressure; Hygrometer: measures atmospheric humidity; Hydrometer: measures liquid density.

Correct Answer: B. Radar

• **Radar** = Radar (Radio Detection And Ranging) emits radio waves that reflect off aircraft, allowing air traffic control to track their range, speed, and direction. • **radio waves** — Radar waves travel at light speed and can operate through clouds, darkness, and fog, making it indispensable for aviation safety. • 💡 Wrong-option analysis: Lidar: uses laser pulses (not for aircraft detection in ATC); Photometer: measures light intensity, not aircraft position; Sonar: uses sound waves and works underwater, not in air.

Correct Answer: B. Viscometer

• **Viscometer** = A viscometer measures the viscosity (resistance to flow) of a liquid by measuring the force required to move one layer of fluid relative to another. • **poise (CGS) / Pa·s (SI)** — Honey has high viscosity (~10,000 mPa·s), water has low viscosity (~1 mPa·s); viscosity data is critical in oil, paint, and food industries. • 💡 Wrong-option analysis: Dilatometer: measures thermal expansion of materials; Venturimeter: measures fluid flow rate in a pipe; Spherometer: measures radius of curvature of spherical surfaces.

Correct Answer: A. Studying the frequency of vibration of strings

• **Studying the frequency of vibration of strings** = A sonometer is a laboratory instrument with a taut wire over a hollow wooden box, used to study how frequency depends on length, tension, and mass per unit length. • **laws of vibrating strings** — It demonstrates Melde's laws: frequency ∝ 1/length ∝ √tension ∝ 1/√linear density, fundamental principles in musical acoustics. • 💡 Wrong-option analysis: Measuring humidity: done by a hygrometer; Measuring sound speed: done using resonance tubes or oscilloscopes; Measuring ocean depth: done by a fathometer (echo sounder).

Correct Answer: B. Nephelometer

• **Nephelometer** = A nephelometer measures the concentration of suspended particles in a liquid or gas by quantifying light scattered at 90° to the incident beam. • **turbidity units (NTU)** — Water clarity is expressed in nephelometric turbidity units (NTU); drinking water standards require turbidity below 1 NTU. • 💡 Wrong-option analysis: Manometer: measures gas or liquid pressure; Barometer: measures atmospheric pressure; Altimeter: measures altitude.

Correct Answer: D. Dilatometer

• **Dilatometer** = A dilatometer measures the change in volume or length of a material caused by temperature changes, used in materials science to study thermal expansion. • **coefficient of thermal expansion** — It measures the coefficient of linear or volumetric thermal expansion α; metals typically expand ~10–20 ppm/°C. • 💡 Wrong-option analysis: Thermometer: measures temperature only, not dimensional change; Calorimeter: measures heat energy absorbed or released; Pyrometer: measures high surface temperatures remotely.

Correct Answer: B. Dynamometer

• **Dynamometer** = A dynamometer measures the torque and rotational speed of an engine to calculate its power output (in horsepower or kilowatts). • **P = 2πNT/60** — Power P = 2πNT/60 where N is RPM and T is torque in N·m; used extensively in automotive testing to rate engine performance. • 💡 Wrong-option analysis: Galvanometer: measures very small electric currents; Hydrometer: measures liquid density; Audiometer: evaluates hearing sensitivity.

Correct Answer: B. Cryometer

• **Cryometer** = A cryometer is a specialised thermometer designed to measure temperatures close to absolute zero (−273.15°C), used in cryogenics research. • **absolute zero** — At these extreme temperatures, conventional liquid thermometers fail because liquids freeze; cryometers use resistance thermometers or gas thermometers. • 💡 Wrong-option analysis: Pyrometer: measures very HIGH temperatures (>600°C) remotely; Thermometer: works for normal temperature range but not cryogenic; Bolometer: measures electromagnetic radiation power.

Correct Answer: C. Hydrometer

• **Hydrometer** = A hydrometer measures the relative density of liquids by floating in them; it sinks deeper in less dense liquids and floats higher in denser ones. • **Archimedes' principle** — Based on Archimedes' buoyancy principle; used to test battery acid, alcohol content, and antifreeze concentration in radiators. • 💡 Wrong-option analysis: Fathometer: measures ocean depth using sound; Hygrometer: measures atmospheric humidity; Manometer: measures gas or liquid pressure.