Scientific Instruments — Set 4

Correct Answer: D. Voltmeter

• **Voltmeter** = A voltmeter measures the electrical potential difference (voltage) between two points in a circuit; it is always connected in parallel. • **high resistance** — An ideal voltmeter has infinite resistance so it draws negligible current and does not disturb the circuit being measured. • 💡 Wrong-option analysis: Ohmmeter: measures electrical resistance; Galvanometer: detects very small currents (not typically potential difference); Ammeter: measures current (connected in series).

Correct Answer: A. Magnetometer

• **Magnetometer** = A magnetometer measures the strength and direction of magnetic fields; it is used in geological surveys, archaeology, and space exploration. • **geophysical surveys** — Magnetometers detect buried mineral deposits and ancient artefacts; spacecraft carry them to study the magnetic environment of other planets. • 💡 Wrong-option analysis: Photometer: measures light intensity; Electrometer: measures electric potential or charge; Hygrometer: measures atmospheric humidity.

Correct Answer: A. Recording and reproducing speech

• **Recording and reproducing speech** = A dictaphone records spoken words onto a storage medium for later playback and transcription, used in business and legal settings. • **voice recorder** — Originally a trademark name, 'dictaphone' became a generic term for voice recorders; digital versions have now replaced analogue tape-based models. • 💡 Wrong-option analysis: Measuring sound waves: done by an oscilloscope or sound level meter; Measuring light speed: done by Fizeau's or Michelson's apparatus; Measuring water depth: done by a fathometer.

Correct Answer: C. Rain Gauge

• **Rain Gauge** = A rain gauge is a meteorological instrument that collects and measures liquid precipitation in millimetres over a set area and time period. • **millimetres (mm)** — Rainfall is reported in mm depth; 1 mm of rain equals 1 litre of water per square metre; accurate data is essential for flood management and agriculture. • 💡 Wrong-option analysis: Barometer: measures atmospheric pressure; Hygrometer: measures humidity (water vapour in air, not rain); Hydrometer: measures the density of liquids.

Correct Answer: B. Microscope

• **Microscope** = A microscope uses lenses (optical) or electron beams (electron microscope) to magnify objects too small to be seen by the naked eye. • **electron microscope** — Optical microscopes magnify up to ~1,000×, while electron microscopes can resolve structures at the atomic level (0.1 nm resolution). • 💡 Wrong-option analysis: Periscope: views objects above obstacles using mirrors; Telescope: magnifies distant objects; Stroboscope: produces flashing light to study fast-moving objects.

Correct Answer: C. Loudspeaker

• **Loudspeaker** = A loudspeaker is a transducer that converts electrical audio signals into sound waves by vibrating a diaphragm using a coil and magnet. • **electromagnetic induction** — An alternating current in the voice coil interacts with the permanent magnet field, causing the cone to move and create pressure waves in air. • 💡 Wrong-option analysis: Generator: converts mechanical energy into electrical energy; Microphone: converts sound energy into electrical energy (opposite of loudspeaker); Transformer: transfers electrical energy between circuits at different voltages.

Correct Answer: D. Venturimeter

• **Venturimeter** = A venturimeter measures the flow rate of fluids in a pipe by applying the Bernoulli principle: the pressure drops as the pipe narrows and the fluid speeds up. • **Bernoulli principle** — Flow rate Q = A₁A₂√(2gh/(A₁²−A₂²)); widely used in water distribution systems and chemical processing industries. • 💡 Wrong-option analysis: Spherometer: measures curvature of spherical surfaces; Dilatometer: measures thermal expansion of materials; Viscometer: measures viscosity (resistance to flow), not flow rate.

Correct Answer: A. Photometer

• **Photometer** = A photometer measures the intensity (luminous flux per unit area) of electromagnetic radiation, including visible light. • **lux meter** — In photography, a light meter (photometer) determines correct exposure; in science, it compares the intensity of an unknown source to a standard source. • 💡 Wrong-option analysis: Pyrheliometer: measures solar irradiance specifically (direct sunlight), not general light intensity; Lactometer: measures specific gravity of milk; Altimeter: measures altitude of aircraft.

Correct Answer: C. To hear sounds produced within the body

• **To hear sounds produced within the body** = A stethoscope is an acoustic medical device that amplifies internal body sounds (heart and lung sounds) and transmits them to the clinician's ears. • **1816 invention** — René Laennec invented the first stethoscope in 1816 using a rolled paper tube; it detects abnormalities like heart murmurs and breathing irregularities. • 💡 Wrong-option analysis: To check blood sugar: done by a glucometer; To measure body height: done by a stadiometer or measuring tape; To view internal organs: done by an endoscope or ultrasound.

Correct Answer: A. Ohmmeter

• **Ohmmeter** = An ohmmeter measures the electrical resistance of a component by passing a small known current through it and measuring the resulting voltage. • **R = V/I** — Based on Ohm's law (R = V/I); most modern multimeters include an ohmmeter function and display resistance in ohms (Ω). • 💡 Wrong-option analysis: Ammeter: measures electric current; Wattmeter: measures electrical power in watts; Voltmeter: measures potential difference in volts.