AP EAMCET / TS EAMCET Physics - Electromagnetism and Modern Physics Syllabus

State the expression for the magnetic force on a moving charge (Lorentz force).

F = q(v × B), magnitude F = qvB·sinθ, where θ is the angle between velocity and field. The force is perpendicular to both v and B and does no work on the charge.

State Biot–Savart law.

The magnetic field due to a small current element is dB = (μ₀/4π)·(I·dl × r̂)/r². It gives the field contribution of a current element I·dl at distance r.

Give the magnetic field at the centre of a circular current loop of radius R.

B = μ₀I/(2R) at the centre, directed along the axis. For N turns, B = μ₀NI/(2R).

State Ampere's circuital law and give the field inside a long solenoid.

Ampere's law: ∮B·dl = μ₀·I_enclosed. For a long solenoid, B = μ₀nI, where n is the number of turns per unit length; the field is uniform inside and nearly zero outside.

Give the force per unit length between two parallel current-carrying conductors.

F/L = μ₀I₁I₂/(2πd), where d is the separation. The force is attractive for currents in the same direction and repulsive for opposite directions. This defines the ampere.

What is the principle and conversion of a galvanometer into an ammeter and voltmeter?

A galvanometer deflects in proportion to current. To make an ammeter, a low resistance (shunt) is connected in parallel. To make a voltmeter, a high resistance is connected in series.

Define magnetic dipole moment of a current loop.

m = N·I·A, where N is number of turns, I the current and A the loop area. It is a vector perpendicular to the loop plane (right-hand rule). SI unit: A·m².

Compare diamagnetic, paramagnetic and ferromagnetic materials.

Diamagnetic: weakly repelled, relative permeability μ_r slightly < 1 (e.g., Bi, Cu). Paramagnetic: weakly attracted, μ_r slightly > 1 (e.g., Al, Pt). Ferromagnetic: strongly attracted, μ_r >> 1, show hysteresis (e.g., Fe, Co, Ni).

State Curie's law for paramagnetic materials.

The magnetization (or susceptibility) of a paramagnetic material is inversely proportional to its absolute temperature: χ = C/T, where C is the Curie constant. Above the Curie temperature, ferromagnets become paramagnetic.

State Faraday's laws of electromagnetic induction.

First law: a changing magnetic flux through a circuit induces an EMF. Second law: the induced EMF equals the negative rate of change of flux, ε = −dΦ/dt (for N turns, ε = −N·dΦ/dt).

State Lenz's law and the conservation principle it expresses.

The induced current always flows in a direction so as to oppose the change in magnetic flux that produces it. It is a consequence of conservation of energy (the negative sign in Faraday's law).

Define self-inductance and give the EMF it produces.

Self-inductance L is the property of a coil to oppose changes in its own current: Φ = LI. The induced EMF is ε = −L·(dI/dt). SI unit: henry (H).

Give the motional EMF induced in a rod of length l moving with velocity v perpendicular to a field B.

ε = Blv, when v, l and B are mutually perpendicular. This arises from the magnetic force on the free charges in the moving rod.

For an AC source, define RMS value of current and its relation to peak value.

The RMS (root-mean-square) value is the equivalent DC value producing the same heating effect: I_rms = I₀/√2 ≈ 0.707·I₀, where I₀ is the peak current. Similarly V_rms = V₀/√2.

Define inductive reactance and capacitive reactance in an AC circuit.

Inductive reactance X_L = ωL = 2πfL (increases with frequency). Capacitive reactance X_C = 1/(ωC) = 1/(2πfC) (decreases with frequency). Both are measured in ohms.

Give the impedance and resonance condition of a series LCR circuit.

Impedance Z = √[R² + (X_L − X_C)²]. Resonance occurs when X_L = X_C, giving minimum impedance Z = R and maximum current. Resonant frequency f₀ = 1/(2π√(LC)).

Define power factor in an AC circuit.

Power factor = cosφ = R/Z, the ratio of true power to apparent power, where φ is the phase angle between voltage and current. Average power P = V_rms·I_rms·cosφ. It is 1 for a purely resistive circuit and 0 for a purely reactive circuit.

State the principle of a transformer and the transformation ratio.

A transformer works on mutual induction, transferring AC power between coils via a changing flux. V_s/V_p = N_s/N_p = I_p/I_s, where N is the number of turns; for an ideal transformer power is conserved.

List the electromagnetic spectrum in order of increasing frequency.

Radio waves → Microwaves → Infrared → Visible light → Ultraviolet → X-rays → Gamma rays. Frequency increases (and wavelength decreases) along this order.

State the displacement current concept introduced by Maxwell.

Displacement current I_d = ε₀·(dΦ_E/dt) is produced by a changing electric field (e.g., between capacitor plates). Maxwell added it to Ampere's law so that a changing electric field also produces a magnetic field, ensuring continuity of current.

State the speed of electromagnetic waves in vacuum in terms of ε₀ and μ₀.

c = 1/√(μ₀ε₀) ≈ 3 × 10⁸ m/s. EM waves are transverse, with E and B perpendicular to each other and to the direction of propagation, and E/B = c.

State the laws of reflection of light.

1) The incident ray, reflected ray and normal at the point of incidence lie in the same plane. 2) The angle of incidence equals the angle of reflection (i = r).

State Snell's law of refraction and define refractive index.

n₁·sin i = n₂·sin r, where i and r are angles of incidence and refraction. Refractive index n = c/v = (speed of light in vacuum)/(speed in medium); it measures how much a medium bends light.

Define critical angle and the condition for total internal reflection.

Critical angle C is the angle of incidence in the denser medium for which the refraction angle is 90°; sin C = 1/n. Total internal reflection occurs when light travels from a denser to a rarer medium and the angle of incidence exceeds C.

Give the mirror formula and the lens formula.

Mirror formula: 1/v + 1/u = 1/f. Lens formula: 1/v − 1/u = 1/f, where u is object distance, v image distance, f focal length (sign convention applies). Magnification m = h'/h = −v/u (mirror) or v/u (lens).

State the lens maker's formula.

1/f = (n − 1)(1/R₁ − 1/R₂), where n is the refractive index of the lens material relative to surroundings, and R₁, R₂ are the radii of curvature of the two surfaces.

Define power of a lens and its SI unit.

Power P = 1/f (f in metres). SI unit: dioptre (D), 1 D = 1 m⁻¹. Converging (convex) lenses have positive power, diverging (concave) lenses negative power. Powers of lenses in contact add: P = P₁ + P₂.

State the condition for constructive and destructive interference in Young's double-slit experiment.

Constructive (bright fringe): path difference = nλ (n = 0,1,2...). Destructive (dark fringe): path difference = (n + ½)λ. Fringe width β = λD/d, where D is slit-to-screen distance and d the slit separation.

Explain polarization and Brewster's law.

Polarization is the restriction of light's electric field vibrations to one plane, possible only for transverse waves. Brewster's law: when light is incident at the polarizing angle θ_p, the reflected ray is fully polarized and tan θ_p = n (refractive index); the reflected and refracted rays are then perpendicular.

Explain why the sky is blue (Rayleigh scattering).

Rayleigh scattering by air molecules is proportional to 1/λ⁴, so shorter wavelengths (blue) scatter much more than longer (red). The scattered blue light reaches our eyes from all directions, making the sky appear blue; at sunset the long path scatters away blue, leaving red.

State Einstein's photoelectric equation and define work function.

K_max = hν − φ₀, where K_max is the maximum kinetic energy of emitted electrons, hν the photon energy, and φ₀ the work function (minimum energy to release an electron from the metal surface). Threshold frequency ν₀ = φ₀/h.

State the de Broglie hypothesis and give the wavelength formula.

Every moving particle has an associated wave (matter wave) with wavelength λ = h/p = h/(mv), where h is Planck's constant and p the momentum. This expresses the dual (wave–particle) nature of matter.

State Bohr's quantization condition and give the energy of the nth level of hydrogen.

Angular momentum is quantized: L = mvr = nh/(2π). Energy E_n = −13.6/n² eV for hydrogen; the negative sign indicates a bound state, and energy increases (less negative) for higher n.

Give the Rydberg formula for hydrogen spectral lines.

1/λ = R(1/n₁² − 1/n₂²), where R is the Rydberg constant (1.097 × 10⁷ m⁻¹) and n₂ > n₁. Lyman series: n₁=1 (UV); Balmer: n₁=2 (visible); Paschen: n₁=3 (IR).

Define mass defect and binding energy of a nucleus.

Mass defect Δm is the difference between the sum of masses of constituent nucleons and the actual nuclear mass. Binding energy = Δm·c² is the energy needed to split the nucleus into free nucleons; higher binding energy per nucleon means greater stability (maximum near iron).

State the law of radioactive decay and define half-life.

N = N₀·e^(−λt), where λ is the decay constant. Half-life T₁/₂ = 0.693/λ is the time for half the nuclei to decay. Activity A = λN.

Compare nuclear fission and nuclear fusion.

Fission: a heavy nucleus (e.g., U-235) splits into lighter nuclei releasing energy and neutrons; basis of reactors and atom bombs. Fusion: light nuclei (e.g., hydrogen isotopes) combine into a heavier nucleus releasing more energy per nucleon; powers stars, requires very high temperature/pressure.

Distinguish between intrinsic and extrinsic (doped) semiconductors.

Intrinsic: pure semiconductor (Si, Ge) where electrons and holes are equal in number, generated thermally. Extrinsic: doped with impurities — n-type (pentavalent donors, electrons majority) or p-type (trivalent acceptors, holes majority) — giving much higher conductivity.

Explain the working of a p-n junction diode under forward and reverse bias.

Forward bias (p to +, n to −): depletion layer narrows, barrier lowers, large current flows. Reverse bias (p to −, n to +): depletion layer widens, only a tiny saturation current flows. Thus the diode acts as a one-way valve (rectifier).

Differentiate between half-wave and full-wave rectification.

Half-wave rectifier uses one diode and converts only one half of the AC cycle to DC (output during alternate halves). Full-wave rectifier (two diodes with centre-tap, or bridge of four diodes) uses both halves, giving higher efficiency and a smoother, higher-frequency ripple output.

State the role of the three terminals of a transistor and its basic action.

A transistor (npn/pnp) has emitter (heavily doped, supplies carriers), base (thin, lightly doped, controls flow) and collector (collects carriers). A small base current controls a large collector current, enabling amplification and switching; current gain β = I_C/I_B.

State the truth tables of the basic logic gates AND, OR and NOT.

AND: output 1 only when all inputs 1. OR: output 1 when any input is 1. NOT: output is the inverse of input (0→1, 1→0). NAND and NOR are universal gates that can build any logic function.

List the basic elements of a communication system.

Transmitter (converts message into a signal suitable for the channel), communication channel/medium (carries the signal, e.g., wire or space), and receiver (recovers the original message). Noise is the unwanted signal added in the channel.

Define modulation and name its three types for analog signals.

Modulation is superimposing a low-frequency message signal onto a high-frequency carrier wave for efficient transmission. The three types are Amplitude Modulation (AM), Frequency Modulation (FM) and Phase Modulation (PM), depending on which carrier property varies with the message.

Why is modulation necessary, and what determines antenna height for transmission?

Modulation is needed because low-frequency audio signals require impractically large antennas, have low energy and would mix together. A high-frequency carrier allows a practical antenna (length ~λ/4), efficient radiation and multiplexing. Antenna size is set by the wavelength of the carrier.