WavesNEET Physics · Class 11 · NCERT Chapter 14

You can expect 1 to 2 questions from Waves in NEET 2027. The chapter has high PYQ frequency. Wave speed on a string, frequency of standing waves on strings and in pipes, beats and Doppler effect are the favourites.

A traveling wave moving in the positive x direction is y of x and t equals A sin(omega t minus k x), where A is the amplitude, omega is the angular frequency 2 pi f, and k is the wave number 2 pi over lambda. Wave speed v equals omega over k equals f times lambda.

v equals the square root of T over mu, where T is the tension in the string and mu is the linear mass density (mass per unit length, in kg per metre). NEET problems often vary T or change the string and ask how speed changes.

Newton gave v equals square root of B over rho, with B the bulk modulus (isothermal). Laplace corrected this to use the adiabatic bulk modulus, giving v equals square root of gamma P over rho, since the rapid compression in a sound wave is closer to adiabatic than isothermal. For air at 0 degrees C this gives 332 m per s, matching observation.

When two or more waves overlap in a medium, the resulting displacement at every point is the algebraic sum of the displacements due to each individual wave. This single rule explains interference, beats and standing waves.

A standing wave forms when two waves of the same frequency and amplitude travel in opposite directions and superpose. The result has fixed nodes (zero displacement) and antinodes (maximum displacement) that do not propagate. On a string fixed at both ends of length L, allowed wavelengths are lambda_n equals 2 L over n; allowed frequencies are f_n equals n v over (2 L) for n equals 1, 2, 3, ...

When source and observer are moving relative to each other, the observed frequency f_obs differs from the emitted frequency f. For sound: f_obs equals f times (v plus minus v_o) over (v plus minus v_s), with appropriate sign conventions. The frequency goes UP when source and observer approach each other and DOWN when they move apart.