Scientific Instruments — Set 3

Correct Answer: D. Screw Gauge

• **Screw Gauge** = A screw gauge (micrometer screw gauge) measures small distances such as wire diameter or sheet thickness with an accuracy of up to 0.01 mm. • **pitch and least count** — It works on the screw's pitch principle; least count = pitch ÷ number of divisions on the thimble, typically 0.01 mm. • 💡 Wrong-option analysis: Manometer: measures gas or liquid pressure; Tachometer: measures rotational speed; Odometer: measures total distance travelled by a vehicle.

Correct Answer: A. Rotation speed

• **Rotation speed** = A tachometer measures the rotational speed of a shaft or engine disk, usually displayed in revolutions per minute (RPM). • **RPM** — Vehicle dashboards include a tachometer to help the driver select the optimal gear; over-revving beyond the red zone (typically 6,000–8,000 RPM) can damage the engine. • 💡 Wrong-option analysis: Surface tension: measured by a stalagmometer or ring method apparatus; Blood pressure: measured by a sphygmomanometer; Distance traveled: measured by an odometer.

Correct Answer: B. Wattmeter

• **Wattmeter** = A wattmeter measures the active (real) electrical power in watts consumed by a circuit; it combines the functions of a voltmeter and ammeter. • **P = V × I × cos φ** — Power in AC circuits = voltage × current × power factor (cos φ); the wattmeter directly displays this result. • 💡 Wrong-option analysis: Voltmeter: measures potential difference (volts) only; Ammeter: measures electric current (amperes) only; Ohmmeter: measures electrical resistance (ohms).

Correct Answer: C. Electroscope

• **Electroscope** = An electroscope detects the presence and sign of electric charge; the gold-leaf electroscope has two gold leaves that diverge when charged. • **gold-leaf electroscope** — When charged, the two gold leaves repel each other and spread apart; the greater the charge, the wider the divergence. • 💡 Wrong-option analysis: Endoscope: views inside hollow organs using a flexible camera tube; Telescope: views distant objects; Stethoscope: listens to internal body sounds.

Correct Answer: A. Detecting and locating distant objects

• **Detecting and locating distant objects** = RADAR (Radio Detection And Ranging) emits radio waves and analyses the reflected echo to determine the position, distance, and speed of objects. • **radio waves** — Radar uses radio waves that travel at the speed of light (~3 × 10⁸ m/s); it works in darkness and through clouds, making it indispensable for air traffic control. • 💡 Wrong-option analysis: Measuring rainfall: done by a rain gauge; Locating submerged submarines: done by SONAR which uses sound waves, not radio waves; Checking heart rhythm: done by an ECG machine.

Correct Answer: B. Salinometer

• **Salinometer** = A salinometer measures the concentration of salt in water (usually seawater) by measuring electrical conductivity, which increases with dissolved salt content. • **oceanography** — Ocean salinity averages about 35 parts per thousand (ppt); salinometer data is critical for oceanography and industrial boiler maintenance. • 💡 Wrong-option analysis: Photometer: measures light intensity; Fluxmeter: measures magnetic flux; Calorimeter: measures heat of chemical reactions.

Correct Answer: C. Transistor

• **Transistor** = A transistor is a semiconductor device that amplifies or switches electronic signals; a small base current controls a much larger collector current. • **1947 invention** — Invented at Bell Labs in 1947 by Bardeen, Brattain, and Shockley; the transistor replaced vacuum tubes and revolutionised modern electronics. • 💡 Wrong-option analysis: Inductor: stores energy in a magnetic field; resists current changes but does not amplify; Capacitor: stores energy in an electric field; Resistor: reduces current by opposing it, not amplifying.

Correct Answer: C. Calorimeter

• **Calorimeter** = A calorimeter is an insulated container used to measure the heat released or absorbed during chemical reactions or physical processes. • **Q = mcΔT** — Heat is calculated using Q = mcΔT (mass × specific heat × temperature change); bomb calorimeters are used to measure caloric content of food. • 💡 Wrong-option analysis: Thermometer: measures temperature, not heat of reaction; Radiometer: measures radiant energy flux; Pyrometer: measures very high surface temperatures remotely.

Correct Answer: D. Distance traveled

• **Distance traveled** = An odometer records the cumulative distance travelled by a vehicle since manufacture, displayed on the dashboard. • **maintenance tracking** — Odometer readings are essential for scheduling vehicle servicing (e.g., oil change every 5,000 km) and determining resale value. • 💡 Wrong-option analysis: Engine temperature: measured by an engine coolant temperature gauge; Current speed: measured by a speedometer; Fuel level: measured by a fuel gauge.

Correct Answer: C. Endoscope

• **Endoscope** = An endoscope is a flexible tube with a fibre-optic camera that allows doctors to visually examine the inside of hollow organs. • **minimally invasive** — Used in colonoscopy, gastroscopy, and laparoscopy; it enables diagnosis and minor surgery without large incisions, reducing patient recovery time. • 💡 Wrong-option analysis: Gyroscope: determines orientation and angular velocity; Stethoscope: listens to internal sounds (not images); Microscope: magnifies tiny specimens on slides, not live internal organs.