NEB Class 12 Physics flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Projectile range

For a projectile launched at speed u and angle θ on level ground, the horizontal range is R = u² sin2θ / g. Range is maximum at θ = 45° and equal for complementary angles.

Centripetal acceleration

An object moving in a circle of radius r at speed v has acceleration v²/r directed toward the centre. This changes only the direction of velocity, never its magnitude.

Parallel axis theorem

The moment of inertia about any axis equals the moment about a parallel axis through the centre of mass plus Md², where M is the mass and d the separation of the axes.

Escape velocity

The minimum launch speed for a body to leave a planet without further propulsion: v = √(2GM/R). It is independent of the projectile's mass and equals √2 times orbital speed near the surface.

Elastic collision

A collision in which both linear momentum and kinetic energy are conserved. For equal masses, one body initially at rest, the incident body stops and the target moves off with its velocity.

First law of thermodynamics

Energy conservation for a thermodynamic system: ΔU = Q − W, where Q is heat added to the gas and W is work done by the gas. Internal energy is a state function.

Carnot efficiency

The maximum efficiency of any heat engine operating between hot and cold reservoirs at absolute temperatures T_h and T_c is η = 1 − T_c/T_h.

Adiabatic process

A process with no heat exchange, Q = 0, so ΔU = −W. For an ideal gas PV^γ is constant and the gas cools on expansion, where γ = C_p/C_v.

Root mean square speed

For an ideal gas, v_rms = √(3RT/M) = √(3kT/m). It rises with the square root of absolute temperature and falls with increasing molar mass.

Latent heat

Heat absorbed or released per unit mass during a change of phase at constant temperature, Q = mL. For water, the latent heat of fusion is about 3.34 × 10⁵ J/kg.

Snell's law

At a refracting interface, n₁ sinθ₁ = n₂ sinθ₂, where angles are measured from the normal. Light bends toward the normal when entering a denser medium.

Critical angle

The angle of incidence in the denser medium for which the refracted ray grazes the interface, given by sinθ_c = n₂/n₁. Beyond it, total internal reflection occurs.

Young's double slit fringes

Two coherent sources separated by d produce on a screen at distance D fringes of spacing β = λD/d. Bright fringes occur where the path difference is a whole number of wavelengths.

Malus's law

When plane-polarised light of intensity I₀ passes through an analyser whose axis makes angle θ with the polarisation direction, the transmitted intensity is I = I₀ cos²θ.

Brewster's angle

At the polarising angle of incidence, tanθ_B = n₂/n₁, the reflected ray is completely polarised perpendicular to the plane of incidence and reflected and refracted rays are 90° apart.

Lens maker's formula

For a thin lens of refractive index n and radii R₁, R₂: 1/f = (n − 1)(1/R₁ − 1/R₂). Power in dioptres is P = 1/f with f in metres.

Gauss's law

The total electric flux through any closed surface equals the enclosed charge divided by ε₀. It simplifies fields of symmetric charge distributions such as spheres, cylinders and sheets.

Capacitors in series

Series capacitors carry the same charge and their reciprocal capacitances add: 1/C = 1/C₁ + 1/C₂. The equivalent capacitance is always smaller than the smallest individual capacitance.

Kirchhoff's loop rule

Around any closed circuit loop, the algebraic sum of potential differences is zero. This is a statement of energy conservation for charge carriers traversing the loop.

Wheatstone bridge balance

The bridge is balanced, with no galvanometer current, when the ratio of resistances in one branch equals that in the other: P/Q = R/S. This condition is independent of the applied EMF.

Faraday's law of induction

The induced EMF in a circuit equals the negative rate of change of magnetic flux through it: ε = −dΦ/dt. The minus sign expresses Lenz's law.

Magnetic field of a solenoid

Inside a long solenoid carrying current I with n turns per unit length, B = μ₀nI, nearly uniform and parallel to the axis; outside it is approximately zero.

Photoelectric stopping potential

The reverse voltage V₀ that just stops the fastest emitted photoelectrons: eV₀ = hf − φ. It depends on frequency, not on light intensity.

de Broglie wavelength

A particle of momentum p has an associated wavelength λ = h/p. For an electron accelerated through V volts, λ in ångström is approximately 12.27/√V.

Bohr energy levels

In the hydrogen atom, E_n = −13.6/n² eV. Photon energy emitted in a transition equals the difference between the two level energies, giving discrete spectral lines.

Heisenberg uncertainty principle

Position and momentum of a particle cannot both be known exactly: Δx·Δp ≥ ħ/2, where ħ = h/2π. The limit arises from wave–particle duality, not poor instruments.

Mass defect

The difference between the mass of a nucleus and the sum of its constituent nucleon masses. Multiplied by c², it gives the binding energy holding the nucleus together.

Half-life

The time for half the nuclei in a radioactive sample to decay: t½ = 0.693/λ. After n half-lives, the fraction remaining is (1/2)^n.

Beta-minus decay

A neutron-rich nucleus converts a neutron into a proton, emitting an electron and an antineutrino. The mass number is unchanged while the atomic number increases by one.

p-n junction depletion region

A zone at the junction where diffusion of carriers leaves fixed ionised dopants and a built-in electric field. Forward bias narrows it; reverse bias widens it.

Transistor current gain

In a transistor, emitter current equals base plus collector current, I_E = I_B + I_C. Common-emitter current gain is β = I_C/I_B, typically 20 to 500.

NAND gate as universal gate

The NAND gate outputs 0 only when all inputs are 1. Any logic function can be built from NAND gates alone, so it is called a universal gate.