Physics

Internal friction in a fluid is known as viscosity, which measures the fluid's resistance to flow. Surface tension, resistance, and cohesive force are different physical properties and do not describe internal friction.

Isaac Newton proposed the corpuscular theory of light, suggesting that light is made up of small particles called corpuscles. This theory was prominent before the wave theory of light gained acceptance.

The nuclear radius is extremely small, typically on the order of femtometers (also called fermis), which is 10^-15 meters. Therefore, the most suitable unit to express nuclear radius is the fermi (option D). Angstroms, micrometers, and nanometers are too large for this scale.

In vacuum, all electromagnetic waves (ultraviolet, infrared, microwave) travel at the same speed, the speed of light (approximately 3.0 × 10^8 m/s). Sound waves are mechanical waves that require a medium (like air, water, or solids) to propagate. Since vacuum has no medium, sound cannot travel in vacuum and effectively has zero velocity there. Therefore, among the options, sound has the smallest velocity in vacuum, which is zero.

The turning effect of a force about a pivot point is called torque. While 'moment' is also used in physics to describe turning effect, 'torque' is the more precise term in this context. 'Momentum' refers to mass in motion, which is unrelated to turning effects.

The SI unit of volume is the cubic meter (m³), which is the volume of a cube with edges one meter in length. Options B, C, and D represent cubic centimeters, cubic millimeters, and cubic kilometers respectively, which are not the SI base unit but derived units.

Torque is the measure of rotational force and in the International System of Units (SI), it is expressed in Newton-meters (N·m), which combines force (Newton) and distance (meter).

Damping is the process by which energy is gradually lost from an oscillating system, causing the amplitude of oscillations to decrease over time.

Geophysics is the branch of physics that studies the physical properties and internal structure of the Earth, including its composition and processes. The other options do not focus on Earth's internal structure.

According to quantum theory, photons are quanta of electromagnetic radiation, meaning they are discrete packets of energy. Each photon carries an energy proportional to its frequency (E = hν). Photons exhibit both particle-like and wave-like properties, embodying the wave-particle duality of light. They are massless particles that travel at the speed of light and are the fundamental quanta of the electromagnetic field. Thus, describing photons as 'energy packets' is accurate and captures their quantum nature. While photons also have particle and electromagnetic wave characteristics, the term 'energy packets' best reflects the quantum theory perspective.