Tamil Nadu HSE Second Year Physics flashcards

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

Coulomb's law in medium

The force between two point charges in a medium is F = q1 q2 / (4π ε0 εr r²), directed along the line joining them; εr is the relative permittivity.

Electric field of point charge

At distance r from a point charge Q, the electric field is E = Q/(4π ε0 r²). It points radially outward for positive Q and inward for negative Q.

Gauss law application

The total electric flux through a closed surface equals enclosed charge divided by ε0. For a charged conducting sphere, field outside behaves as a point charge; inside it is zero.

Capacitors in series and parallel

Series capacitors have the same charge and reciprocal capacitances add: 1/C = 1/C1 + 1/C2. Parallel capacitors have the same voltage and capacitances add: C = C1 + C2.

Drift velocity relation

Drift velocity vd is related to current by I = n A e vd, where n is free-electron density, A is cross-sectional area, and e is electronic charge. Current density J = n e vd.

Resistivity formula

Resistance R of a conductor is R = ρL/A, where ρ is resistivity, L is length and A is cross-sectional area. Resistivity depends on material and temperature, not on dimensions.

Kirchhoff circuit rules

The junction rule states that the algebraic sum of currents at a node is zero. The loop rule states that around any closed circuit the sum of emf values equals the sum of IR drops.

Wheatstone bridge balance

A Wheatstone bridge is balanced when the galvanometer shows no deflection. Then R1/R2 = R3/R4; the product of opposite arms is equal and no current flows through the galvanometer.

Magnetic force on charge

A charge q moving with velocity v in magnetic field B experiences F = q(v × B). The magnitude is qvB sinθ, and the force is perpendicular to both v and B.

Circular motion in magnetic field

A charged particle entering perpendicular to a uniform magnetic field moves in a circle of radius r = mv/(qB). Its period T = 2πm/(qB) is independent of speed.

Biot-Savart law

The magnetic field due to a current element is dB = (μ0/4π) I dl sinθ / r²; its direction follows the right-hand rule and is perpendicular to the element and radius vector.

Moving coil galvanometer

In a moving-coil galvanometer, a current-carrying coil in a radial magnetic field experiences a torque. The deflection is proportional to current: I = kθ, where k is the galvanometer constant.

Faraday law of induction

The induced emf in a circuit equals the negative rate of change of magnetic flux: ε = -dΦ/dt. The minus sign represents Lenz's law, opposing the change in flux.

Self-inductance energy

A coil with self-inductance L carrying current I stores magnetic energy U = ½LI². Self-induced emf is ε = -L dI/dt, opposing any change in current.

Series LCR resonance

In a series LCR circuit, resonance occurs at angular frequency ω0 = 1/√(LC). At resonance, inductive and capacitive reactances cancel, impedance is minimum and equals R, and current is maximum.

Transformer voltage ratio

For an ideal transformer, Vs/Vp = Ns/Np, where V and N denote voltage and turns. Power input equals power output, so a step-up transformer raises voltage and lowers current.

Mirror formula

For a spherical mirror, 1/f = 1/v + 1/u, with f = R/2. Magnification m = -v/u. The Cartesian sign convention assigns distances measured against incident light as negative.

Lens formula and power

For a thin lens, 1/f = 1/v - 1/u, and magnification m = v/u. Power P = 1/f in dioptres when f is in metres; converging lenses have positive power.

Young double-slit fringe width

In Young’s double-slit experiment, the fringe width is β = λD/d, where λ is wavelength, D is slit-screen distance and d is slit separation. Bright fringes occur at path difference nλ.

Total internal reflection

Total internal reflection occurs when light travels from a denser to a rarer medium and the angle of incidence exceeds the critical angle C, where sin C = 1/n. No refracted ray emerges.

Photon energy relation

A photon of frequency ν has energy E = hν = hc/λ, where h is Planck’s constant and c is light speed. Its momentum is p = h/λ.

Einstein photoelectric equation

Maximum kinetic energy of a photoelectron is Kmax = hν - W, where W is the work function. Equivalently, eV0 = hν - hν0, with V0 the stopping potential.

de Broglie wavelength

A particle of mass m moving with speed v has matter wavelength λ = h/(mv) = h/√(2mK), where K is kinetic energy. Electron diffraction confirms this wave nature.

Bohr energy levels

For hydrogen-like atoms, En = -13.6 Z²/n² eV. The radius is rn = 0.529 n²/Z Å, and spectral lines arise from transitions between levels with hν = E2 - E1.

Radioactive decay law

Radioactive decay follows N = N0e^(-λt), where λ is decay constant. Half-life T1/2 = 0.693/λ, and activity A = λN decreases exponentially with the same half-life.

Mass defect and binding energy

Mass defect Δm is the difference between the sum of separate nucleon masses and the nucleus mass. Binding energy is Δm c²; binding energy per nucleon peaks near iron-56.

Nuclear fission and fusion

Fission splits a heavy nucleus into lighter nuclei with release of energy and neutrons. Fusion combines light nuclei, as in the Sun, and releases energy because binding energy per nucleon increases.

PN junction forward bias

Forward bias connects p to positive and n to negative. It reduces the depletion barrier, allowing majority carriers to cross, so current increases rapidly above the knee voltage.

Transistor current gain

For a transistor, α = IC/IE and β = IC/IB. The relation is β = α/(1 - α), so a small base current controls a much larger collector current in CE configuration.

NAND and NOR gates

NAND outputs low only when all inputs are high; NOR outputs high only when all inputs are low. Each is a universal gate, capable of building NOT, AND, OR and any logic circuit.

Amplitude modulation index

In amplitude modulation, the modulation index m = Am/Ac, where Am is modulating amplitude and Ac is carrier amplitude. Percentage modulation is 100m, and AM bandwidth is twice the modulating frequency.

Need for modulation

Modulation allows efficient radiation using antennas of practical height, avoids mixing of signals by assigning different carrier frequencies, and enables multiplexing of many baseband signals over one channel.