Physics Basics — Set 1

Correct Answer: A. Mass

• **Mass** = Mass is a scalar quantity because it has only magnitude and no direction. • **constant** — Mass remains constant regardless of the object's position in the universe. • 💡 Wrong-option analysis: Velocity: has both magnitude and direction, so it is a vector; Acceleration: involves direction of change in velocity, so it is a vector; Displacement: measures distance in a specific direction, making it a vector.

Correct Answer: A. Candela

• **Candela** = The candela is the SI unit used to measure luminous intensity in a given direction from a light source. • **7** — Candela is one of the 7 fundamental base units of the International System of Units. • 💡 Wrong-option analysis: Ampere: measures electric current, not light; Kelvin: measures thermodynamic temperature; Mole: measures amount of substance.

Correct Answer: D. Isaac Newton

• **Isaac Newton** = Isaac Newton formulated the Law of Universal Gravitation in 1687, stating every mass attracts every other mass. • **1687** — He published this law in his landmark work 'Philosophiae Naturalis Principia Mathematica' in 1687. • 💡 Wrong-option analysis: Galileo Galilei: studied motion and falling bodies, but did not formulate universal gravitation; Johannes Kepler: described planetary motion laws, not gravitational force; Albert Einstein: developed the theory of relativity, which extended but did not discover Newton's law.

Correct Answer: D. Barometer

• **Barometer** = A barometer is a scientific instrument used specifically to measure atmospheric pressure. • **1643** — The mercury barometer was invented by Evangelista Torricelli in 1643. • 💡 Wrong-option analysis: Thermometer: measures temperature, not pressure; Anemometer: measures wind speed; Hygrometer: measures humidity in the air.

Correct Answer: C. Second

• **Second** = The second is the base unit of time in the International System of Units (SI). • **cesium-133** — The second is defined by the transition frequency of the cesium-133 atom. • 💡 Wrong-option analysis: Minute: equals 60 seconds, so it is a derived unit of time, not a base SI unit; Hour: equals 3600 seconds, not a base SI unit; Day: equals 86400 seconds, not a base SI unit.

Correct Answer: B. Optics

• **Optics** = Optics is the branch of physics that studies the behavior and properties of light, including reflection and refraction. • **reflection** — Modern optics includes laser physics and fiber optic communication based on total internal reflection. • 💡 Wrong-option analysis: Thermodynamics: deals with heat and energy transfer; Mechanics: studies motion and forces on bodies; Acoustics: deals with sound and its propagation.

Correct Answer: C. Wilhelm Röntgen

• **Wilhelm Röntgen** = Wilhelm Röntgen discovered X-rays in 1895 while experimenting with cathode ray tubes in his laboratory. • **1901** — He received the very first Nobel Prize in Physics in 1901 for this discovery. • 💡 Wrong-option analysis: J.J. Thomson: discovered the electron in 1897; Ernest Rutherford: discovered the atomic nucleus and proton; Marie Curie: pioneered research on radioactivity but did not discover X-rays.

Correct Answer: C. Ampere

• **Ampere** = The ampere is the standard SI base unit of electric current, named after André-Marie Ampère. • **1 coulomb/second** — One ampere is defined as the flow of one coulomb of electric charge per second. • 💡 Wrong-option analysis: Ohm: measures electrical resistance; Watt: measures power (rate of energy use); Volt: measures electric potential difference.

Correct Answer: B. Volume

• **Volume** = Volume is a derived quantity because it is calculated by multiplying three lengths (length × width × height). • **m³** — The SI unit of volume is the cubic meter (m³), derived from the base unit meter. • 💡 Wrong-option analysis: Luminous intensity: is a base SI quantity measured in candela; Temperature: is a base SI quantity measured in kelvin; Length: is a fundamental base SI quantity measured in meter.

Correct Answer: D. Astronomical distance

• **Astronomical distance** = A parsec is a unit of length used to measure large distances to astronomical objects outside the Solar System. • **3.26 light-years** — One parsec is approximately equal to 3.26 light-years, or about 3.086 × 10¹⁶ meters. • 💡 Wrong-option analysis: Brightness: is measured in candela or magnitude; Time: is measured in seconds in the SI system; Mass: is measured in kilograms in the SI system.