NEET Physics Sound And Light Waves Revision Notes

Download the latest NEET Physics Sound And Light Waves Revision Notes in PDF format. These Full Course Sound and Light Waves revision notes are carefully designed by expert teachers to align with the 2026-27 syllabus. These notes are great daily learning and last minute exam preparation and they simplify complex topics and highlight important definitions for Full Course students.

Revision Notes for Full Course Sound and Light Waves Sound And Light Waves

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Sound And Light Waves Revision Notes for Full Course Sound and Light Waves

 

Sound Waves:-
 
It is the form of energy which produces, in us, the sensation of hearing.
 
• Properties:-
 
(a) Longitudinal in nature.
(b) It requires a material medium for its propagation.
(c) Sound waves can be reflected.
(d) Sound waves suffer refraction.
(e) Sound waves show the phenomenon of interference
(f) Sound waves shows diffraction
(g) Sound propagates with a velocity much smaller than that of light.
(h) Sound gets absorbed in the medium through which it passes.
 
• Loudness (L)or Intensity (I):-
 
NEET Physics Sound and Light Waves Revision Notes
Unit of intensity of sound is bel.
 
• Intensity (I) and Amplitude (A):-
NEET Physics Sound and Light Waves Revision Notes-1
 
• Intensity(I) and distance from the source (r):-
NEET Physics Sound and Light Waves Revision Notes-2
 
•  Pitch or Shrillness:-Pitch is a sensation which determines the shrillness of sound. It is subjective and cannot be measured quantitatively. It depends up on frequency and relative motion
between the sources and the listener.
•  Quality or Timber:- It is that characteristic of a musical sound which enables us to distinguish between two notes of the same pitch and loudness produced by two different sources.
 
•  Velocity u of longitudinal wave (sound) [Newton’s Formula]:-
u = √E/ρ
Here E is the coefficient of elasticity and ρ is the density of medium.
 
•  Velocity of sound in solids:-
u = √Y/ρ
Here Y is the young’s modulus of elasticity and ρ is the density.
 
• Velocity of sound in liquids:-
u = √B/ρ
Here B is the Bulk modulus of elasticity and ρ is the density.
 
• Velocity of sound in gases:-
u = √γP/ρ
Here, γ (=cP/cV) is the adiabatic ratio, P is the pressure and ρ is the density.
 
• Various factors affecting velocity of sound:-
(a) Effect of density:- The velocity of sound in a gas varies inversely as the square root of its
density. u1/ u2 = √*ρ2/ρ1]
 
(b) Effect of moisture:-um/ud= √*ρd/ ρm]
Since, ρm<ρd, then, um>ud
This signifies sound travels faster in moist air.
 
(c) Effect of pressure:- u=√γP/ρ=√γk = constant
This signifies, change of pressure has no effect on the velocity of sound.
 
(d) Effect of temperature:- ut/u0 =√ρ0/ρt= √T/T0
Thus, velocity of sound varies directly as the square root temperature on Kelvin’s scale.
 
(e) Temperature coefficient of velocity of sound (α):- α = u0/546 = (ut-u0)/t
 
• Overtones in open pipe:-An open pipeis open at both ends. Since air is free to vibrate at an open end, we must get an antinode at the open end
NEET-Physics-Sound-and-Light-Waves-Revision-Notes-unlocked 1
(a) Fundamental frequency:-
Wavelength, λ=2l
Frequency, f=u/2l = (1/2l)√(γP/ρ)
Here l is the length of the pipe and u is the velocity of sound.
 
(b) First overtone (Second Harmonic):-
Wavelength, λ1=l
Frequency, f1=2f
c) Second overtone (Third Harmonic):-
Wavelength, λ2=2l/3
Wavelength, f2=3f
 
• Overtones in closed pipe:-Since air, at a closed end, is not free to vibrate, there must be a node at a closed end always.
NEET-Physics-Sound-and-Light-Waves-Revision-Notes-unlocked 2
(a) Fundamental frequency:-
Wavelength, λ=4l
Frequency, F=u/4l = (1/4l)√(γP/ρ)
Here l is the length of the pipe and u is the velocity of sound.
 
(b) First overtone (Third Harmonic):-
Wavelength, λ1=(4/3)l
Frequency, F1=3F
 
(c) Second overtone (Fifth Harmonic):-
λ2 = 4l/5
F2 = 5F
• Comparison of fundamental frequencies of a closed end of an open pipe:- f = 2F
• Doppler’s Effect:-Theapparent change in pitch of a note, due to the relative motion between the source and the listener is called Doppler’s effect.
 
(a) Source in motion, listener at rest:-
 
(i) Source approaching the listener:-
Modifying wave length, λ' = V-a/f
Apparent frequency, f' = [V/V-a]f
Change in frequency, ?f = (a/V-a)f
 
Here V is the velocity of sound in air and a is the velocity of source when it moves towards the listener.
 
(ii) Source going away from the listener:-
Apparent frequency, f' = [V/V+a]f
Change in frequency, ?f = -(a/V+a)f
 
(iii) Source crossing the listener:-
Apparent frequency of the source before crossing = (V/V-a) f
Apparent frequency of the source after crossing = (V/V+a) f
Change in frequency, ?f = -(2aV/V2-a2)f
 
(b) Source at rest, listener in motion:-
 
(i) Listener moving away from source:-
Apparent frequency, f'= [V-b/V]f
Change in frequency, ?f = (-b/V)f
Here b is the velocity of listener.
 
(ii) Listener moving towards the source:-
Apparent frequency:-f'= [V+b/V]f
Change in frequency, ?f = (+b/V)f
 
(iii) Listener crossing the source:-
Apparent frequency of the source before crossing = (V+b/V) f
Apparent frequency of the source after crossing = (V-b/V) f
Change in frequency, ?f =-2fb/V
 
 
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NEET Full Course Sound and Light Waves Sound And Light Waves Notes

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