NCERT Physics Class XII Part II Vocabulary Review

Vocabulary flashcards covering fundamental definitions, principles, and concepts from NCERT Class XII Physics Part II textbook.

Light

Electromagnetic radiation belonging to the region of the spectrum detected by the human retina, with wavelengths ranging from about $400\,nm$ to $750\,nm$.

Ray of Light

The straight-line path along which a light wave is considered to travel from one point to another.

Corpuscular Model of Light

A light model developed by Isaac Newton proposing that light energy is concentrated in tiny, massless, elastic particles called corpuscles.

Principal Focus

The point $F$ on the principal axis of a spherical mirror where reflected paraxial rays parallel to the principal axis converge or appear to diverge.

Focal Length

The distance between the focus $F$ and the pole $P$ of a spherical mirror or optical centre of a lens, given by $f = \frac{R}{2}$ for a mirror of radius $R$.

Snell's Law of Refraction

The law stating that for a given pair of media, the ratio of the sine of the angle of incidence $i$ to the sine of the angle of refraction $r$ is constant, given by $\frac{\sin(i)}{\sin(r)} = n_{21}$.

Critical Angle

The angle of incidence $i_c$ in an optically denser medium for which the angle of refraction in the rarer medium is $90^\circ$, satisfying $\sin(i_c) = n_{21}$.

Total Internal Reflection

The complete reflection of a light ray back into an optically denser medium when incident at an interface with a rarer medium at an angle greater than the critical angle $i_c$.

Power of a Lens

The measure of convergence or divergence a lens introduces on light falling on it, defined as $P = \frac{1}{f}$ with SI unit dioptre ($D$), where $1\,D = 1\,m^{-1}$.

Dispersion

The phenomenon of splitting a beam of white light into its constituent component colors upon passing through a dispersive medium such as a glass prism.

Rayleigh Scattering

The scattering of light by particles much smaller in size than the wavelength $\lambda$, where the amount of scattering is inversely proportional to the fourth power of the wavelength (proportional to $\frac{1}{\lambda^4}$).

Myopia

A visual defect (nearsightedness) where light from distant objects converges at a point in front of the retina, corrected using a concave lens.

Hypermetropia

A visual defect (farsightedness) where incoming light focuses at a point behind the retina, corrected using a convex lens.

Wavefront

The locus of all points in a medium that vibrate or oscillate in the same phase, representing a surface of constant phase.

Huygens Principle

A geometrical construction asserting that every point on a wavefront acts as a source of secondary wavelets spreading in all directions, and the new wavefront is the forward envelope of these wavelets.

Coherent Sources

Two sources of light that emit waves with a constant or zero phase difference over time.

Diffraction

The phenomenon of bending or spreading of light waves around the edges of an obstacle or narrow aperture into the region of geometrical shadow.

Fresnel Distance

The distance $z_F = \frac{a^2}{\lambda}$ beyond which the beam spreading due to diffraction becomes comparable to or dominates over the size $a$ of the aperture.

Brewster's Law

The law stating that when unpolarised light is incident at Brewster's angle $i_B$ such that reflected and refracted rays are perpendicular, the refractive index is $\tan(i_B) = n$.

Work Function

The minimum energy $\phi_0$ required to pull a free electron out from the surface of a metal, measured in electron volts ($eV$).

Photoelectric Effect

The phenomenon of instantaneous emission of electrons from a photosensitive metal surface when illuminated by electromagnetic radiation of frequency above a threshold frequency.

Threshold Frequency

The minimum cutoff frequency $\nu_0 = \frac{\phi_0}{h}$ of incident radiation below which no photoelectric emission takes place from a given photosensitive surface.

de Broglie Wavelength

The wavelength $\lambda = \frac{h}{p} = \frac{h}{m v}$ associated with a moving material particle of mass $m$ and velocity $v$.

Heisenberg Uncertainty Principle

The principle stating that the product of uncertainty in position $\Delta x$ and uncertainty in momentum $\Delta p$ of a particle is on the order of $\hbar$, given by $\Delta x \Delta p \sim \hbar$.

Bohr Radius

The radius $a_0$ of the innermost stationary orbit ($n = 1$) of the hydrogen atom, equal to $a_0 = \frac{\epsilon_0 h^2}{\pi m e^2} \approx 5.29 \times 10^{-11}\,m$.

Ionisation Energy

The minimum energy required to completely remove an electron from the ground state of an atom to infinity, equal to $13.6\,eV$ for a hydrogen atom.

Mass Defect

The difference $\Delta M = [Z m_p + (A - Z) m_n] - M$ between the total mass of individual constituent nucleons and the actual mass $M$ of the bound nucleus.

Binding Energy

The energy $E_b = \Delta M c^2$ required to completely separate a nucleus into its individual constituent nucleons.

Nuclear Fission

A nuclear process in which a heavy nucleus (such as $^{235}_{92}U$) splits into two intermediate-mass fragment nuclei along with neutrons, releasing approximately $200\,MeV$ of energy per event.

Nuclear Fusion

A thermonuclear process in which two light nuclei combine to form a single heavier, more tightly bound nucleus, releasing energy.

Intrinsic Semiconductor

A pure semiconductor material where the concentration of thermally generated conduction electrons $n_e$ equals the concentration of holes $n_h$ ($n_e = n_h = n_i$).

Extrinsic Semiconductor

A semiconductor doped with a small amount of pentavalent or trivalent impurity atoms to significantly alter the concentration of majority charge carriers.

Zener Diode

A heavily doped $p\text{-}n$ junction diode designed to operate continuously in the reverse breakdown voltage region without damage, used as a voltage regulator.

Logic Gate

A digital electronic circuit with one or more input terminals and one output terminal that obeys a specific logical relationship between input and output voltage levels.