Physics Basics — Set 3

Correct Answer: A. Law of Conservation of Energy

• **Law of Conservation of Energy** = The Law of Conservation of Energy states that the total energy of an isolated system remains constant — it can change form but not quantity. • **First Law of Thermodynamics** — This law is also called the First Law of Thermodynamics, applying to all physical and chemical processes. • 💡 Wrong-option analysis: Law of Inertia: states that a body at rest stays at rest unless acted upon — it is Newton's First Law; Law of Reflection: states that angle of incidence equals angle of reflection for light; Ohm's Law: states that current is proportional to voltage in a conductor.

Correct Answer: B. Galvanometer

• **Galvanometer** = A galvanometer is an electromechanical instrument that detects and measures very small electric currents using a deflecting needle. • **microampere** — Galvanometers can detect currents in the microampere range, far more sensitive than a standard ammeter. • 💡 Wrong-option analysis: Ammeter: measures larger currents but is not sensitive enough for very small currents; Voltmeter: measures electric potential difference, not current; Ohmmeter: measures electrical resistance in a circuit.

Correct Answer: B. Henri Becquerel

• **Henri Becquerel** = Henri Becquerel discovered radioactivity in 1896 while studying phosphorescent uranium salts that emitted penetrating rays. • **1896** — He found uranium emitted radiation spontaneously without needing any external energy source. • 💡 Wrong-option analysis: Michael Faraday: discovered electromagnetic induction and laws of electrolysis; Guglielmo Marconi: developed wireless radio telegraphy; James Maxwell: formulated the theory of electromagnetic fields.

Correct Answer: A. Distance

• **Distance** = A light-year is the distance that light travels in a vacuum in one Julian year, used for astronomical distances. • **9.46 × 10¹² km** — One light-year equals approximately 9.46 trillion kilometers, or about 63,241 astronomical units. • 💡 Wrong-option analysis: Time: despite 'year' in the name, light-year measures distance, not time; Intensity: intensity of light is measured in candela; Speed: the speed of light is measured in meters per second.

Correct Answer: C. Dynamo

• **Dynamo** = A dynamo is a generator that converts mechanical energy (rotation) into direct current electrical energy using electromagnetic induction. • **Faraday's law** — Its working is based on Faraday's law of electromagnetic induction, where a rotating coil in a magnetic field produces current. • 💡 Wrong-option analysis: Capacitor: stores electrical energy in an electric field, does not convert mechanical energy; Electric Motor: does the opposite — converts electrical energy into mechanical energy; Transformer: changes voltage levels in AC circuits, does not convert mechanical to electrical energy.

Correct Answer: B. Proton

• **Proton** = The proton is a subatomic particle found in the nucleus of every atom, carrying a positive electric charge of +1. • **atomic number** — The number of protons in an atom determines its atomic number and which chemical element it is. • 💡 Wrong-option analysis: Neutron: has no electric charge — it is neutral; Electron: carries a negative charge of -1; Positron: is the antimatter counterpart of the electron with a positive charge, but is not found in stable atoms.

Correct Answer: A. Dioptre

• **Dioptre** = The power of a lens is measured in dioptres (D), which equals the reciprocal of the focal length in meters. • **P = 1/f** — A lens with a focal length of 0.5 m has a power of 2 dioptres (P = 1/f). • 💡 Wrong-option analysis: Candela: measures luminous intensity; Lumen: measures total luminous flux from a source; Watt: measures power in terms of energy transfer, not optical lens power.

Correct Answer: B. Alexander Graham Bell

• **Alexander Graham Bell** = Alexander Graham Bell was awarded the first US patent for the telephone in 1876 for transmitting human speech electrically. • **1876** — Bell's patent No. 174,465 filed on March 7, 1876, is considered one of the most valuable patents in history. • 💡 Wrong-option analysis: Benjamin Franklin: invented the lightning rod and bifocals, not the telephone; Nikola Tesla: invented the AC motor and contributed to radio; Thomas Edison: improved the telephone transmitter but did not invent it.

Correct Answer: A. 100°C

• **100°C** = At standard atmospheric pressure (101.325 kPa), pure water boils at exactly 100 degrees Celsius. • **100°C = 212°F = 373.15 K** — The boiling point of water serves as a fixed calibration point for the Celsius and Kelvin scales. • 💡 Wrong-option analysis: 32°C: this is the Fahrenheit value for the freezing point of water, not the boiling point; 212°C: this is actually 212°F, the boiling point in Fahrenheit — not Celsius; 0°C: this is the freezing point of water, not the boiling point.

Correct Answer: B. Fathometer

• **Fathometer** = A fathometer measures ocean depth by transmitting sound waves to the seabed and timing the echo return. • **echo sounding** — This technique, called echo sounding or SONAR, calculates depth using the speed of sound in water (~1500 m/s). • 💡 Wrong-option analysis: Chronometer: is a precise timepiece used for navigation; Fluxmeter: measures magnetic flux; Endoscope: is a medical instrument for viewing inside the body.