NEET Practice Questions (MCQs) with Answers & Solutions

The Stefan-Boltzmann constant (σ) is used in the Stefan-Boltzmann law, which relates the total energy radiated per unit surface area of a black body to the fourth power of its temperature (T). The law is expressed as: $$ E = ext{σ} T^4 $$. Here, E is the energy radiated per unit area per unit time, which has the unit of watts per square meter ( ext{W m}^{-2}). To find the unit of σ, we rearrange the equation: $$ ext{σ} = rac{E}{T^4} $$. Since E has the unit of ext{W m}^{-2} and T has the unit of Kelvin (K), the unit of σ is: $$ ext{σ} = rac{W m^{-2}}{K^4} $$, which simplifies to $$ W m^{-2} K^{-4} $$.

Momentum (p) is defined as the product of mass (m) and velocity (v). Mathematically, it is given by: $$ p = m v $$. The unit of mass (m) is kilogram (kg) and the unit of velocity (v) is meter per second ( ext{m/s}). Therefore, the unit of momentum is: $$ [p] = kg imes rac{m}{s} $$, which is also known as a newton-second (N·s).

A light year is a unit of distance. It is defined as the distance that light travels in one year in a vacuum. Light travels at a speed of approximately 299,792,458 meters per second, so in one year, it covers a vast distance. This unit is often used in astronomy to measure the vast distances between stars and galaxies.

The SI unit of momentum is $ kg imes m imes s^{-1} $. Momentum is the product of mass and velocity, where mass is measured in kilograms (kg) and velocity in meters per second (m/s). Hence, the unit of momentum is $ kg imes ms^{-1} $.

Volt per meter (V/m) is the unit of electric field intensity. The electric field intensity is defined as the force experienced by a unit positive charge placed in the field. It can be derived from the potential difference (voltage) divided by the distance (meter).

The unit of surface tension in the SI system is Newton per meter (N/m). Surface tension is defined as the force per unit length and thus has dimensions of force (Newton) divided by length (meter).

The unit of pascal-second (Pa·s) is used to measure the coefficient of viscosity. Viscosity is a measure of a fluid's resistance to flow, and the coefficient of viscosity quantifies this resistance. 1 Pascal-second is equivalent to 1 kg·m⁻¹·s⁻¹.

The unit of joule-second (Js) is used to measure Planck's constant. Planck's constant is a fundamental constant in physics that relates the energy of a photon to its frequency. It is denoted by the symbol \( h \) and its value is approximately \( 6.62607015 \times 10^{-34} \) Js.