Physics Basics — Set 4

Correct Answer: C. Joule

• **Joule** = The Joule is the SI unit for both work and energy, named after physicist James Prescott Joule. • **1 J = 1 N·m** — One Joule equals the work done when a force of one Newton moves an object one meter. • 💡 Wrong-option analysis: Newton: is the SI unit of force, not energy; Pascal: is the SI unit of pressure; Watt: measures power (rate of energy use), not energy itself.

Correct Answer: C. Johannes Kepler

• **Johannes Kepler** = Johannes Kepler published three laws of planetary motion (1609–1619) describing how planets orbit the Sun in ellipses. • **elliptical orbits** — Kepler's First Law states planets follow elliptical orbits with the Sun at one focus. • 💡 Wrong-option analysis: Edmond Halley: is famous for predicting the return of Halley's Comet; Nicolaus Copernicus: proposed the heliocentric model but did not formulate the laws of planetary motion; Tycho Brahe: made highly accurate astronomical observations that Kepler used, but did not formulate these laws.

Correct Answer: A. Convex mirror

• **Convex mirror** = Convex mirrors are used as rear-view mirrors in vehicles because they always produce a smaller, upright image with a wider field of view. • **wider field of view** — A convex mirror's diverging surface allows a driver to see a larger area behind the vehicle. • 💡 Wrong-option analysis: Concave mirror: converges light and is used in headlights and searchlights, not rear-view mirrors; Cylindrical mirror: has curved shape but is not used as a standard rear-view mirror; Plane mirror: gives a full-size image but a much narrower field of view than a convex mirror.

Correct Answer: B. Kelvin

• **Kelvin** = The Kelvin is the SI base unit of thermodynamic temperature, starting from absolute zero. • **0 K = -273.15°C** — At 0 K (absolute zero), all thermal motion of particles theoretically ceases. • 💡 Wrong-option analysis: Celsius: is a common temperature scale but is not the SI base unit; Rankine: is an absolute temperature scale used in engineering, not the SI unit; Fahrenheit: is used mainly in the United States and is not the SI unit.

Correct Answer: C. Pyrometer

• **Pyrometer** = A pyrometer is a non-contact, remote-sensing thermometer that measures very high temperatures by detecting emitted thermal radiation. • **Stefan-Boltzmann law** — Pyrometers use the Stefan-Boltzmann law to calculate temperature from the intensity of emitted radiation. • 💡 Wrong-option analysis: Calorimeter: measures heat exchanged in chemical or physical reactions, not extreme remote temperatures; Bolometer: measures the power of electromagnetic radiation through heating, used in infrared detection; Thermopile: converts temperature differences to voltage, used in sensors but not for measuring solar temperatures.

Correct Answer: B. 9.8 m/s²

• **9.8 m/s²** = The standard acceleration due to gravity on Earth's surface is approximately 9.8 meters per second squared. • **9.80665 m/s²** — The precise standard value is 9.80665 m/s², though it varies slightly with latitude and altitude. • 💡 Wrong-option analysis: 8.9 m/s²: is close but is not the standard accepted value; 10.5 m/s²: is too high and does not match any standard gravity value; 7.4 m/s²: is approximately the surface gravity of Mars, not Earth.

Correct Answer: A. Evangelista Torricelli

• **Evangelista Torricelli** = Evangelista Torricelli, an Italian physicist, invented the mercury barometer in 1643 to measure atmospheric pressure. • **760 mm Hg** = Standard atmospheric pressure equals 760 mm of mercury, a unit still called 'Torr' in his honor. • 💡 Wrong-option analysis: Blaise Pascal: studied fluid pressure and has the SI unit Pascal named after him, but did not invent the barometer; Robert Boyle: formulated Boyle's Law on gas pressure-volume relationship; Anders Celsius: developed the Celsius temperature scale.

Correct Answer: D. Pascal's Law

• **Pascal's Law** = Pascal's Law states that pressure applied to an enclosed fluid is transmitted undiminished to all parts of the fluid and the container walls. • **F₂/F₁ = A₂/A₁** — A hydraulic lift multiplies force: a small force on a small piston creates a large force on a large piston. • 💡 Wrong-option analysis: Hooke's Law: describes elastic deformation of springs and materials, not fluid pressure; Bernoulli's Principle: relates fluid speed to pressure in flowing fluids, not enclosed static fluid; Archimedes' Principle: explains buoyancy (upward force on immersed objects), not hydraulic force multiplication.

Correct Answer: A. Watt

• **Watt** = The Watt is the SI unit of power, defined as one Joule of work done per second. • **1 W = 1 J/s** — Named after James Watt, one Watt equals the rate of energy transfer of one Joule per second. • 💡 Wrong-option analysis: Tesla: is the SI unit of magnetic flux density; Joule: is the SI unit of energy or work, not power; Newton: is the SI unit of force.

Correct Answer: D. Violet

• **Violet** = Violet light has the shortest wavelength (~380–450 nm) and the highest frequency in the visible spectrum. • **380–450 nm** — The visible spectrum runs from about 380 nm (violet) to 750 nm (red), with violet having the highest energy. • 💡 Wrong-option analysis: Green: has a mid-range wavelength of approximately 520–560 nm; Red: has the longest wavelength (~620–750 nm) in the visible spectrum; Yellow: has a wavelength of approximately 570–590 nm, between green and orange.