Question

I cannot understand equations in the chapter- sound

Answer 1

The query is not clear.eventhough I give some relation below.i think this will do for XI std.
if need anything more ,please ask more specific


Frequency

The number of vibrations per second is called frequency.
The SI unit of frequency is hertz (Hz).
The symbol of frequency is ν (nu).

Time period

The time taken to complete one vibration is called time period.
It is denoted by T.
Its SI unit is second (s).
The frequency of a wave is the reciprocal of the time period.
i.e., v = 1/T

Velocity


The distance travelled by a wave in one second is called velocity of the wave or speed of the wave.
Its S.I. unit is metres per second (m/s).
Velocity = Distance travelled/Time taken
⟹ v = λ/T , where λ = wavelength of the wave travelled in one time time period T)
⟹ v = λv (As 1/T = v)
Thus, Velocity = Wavelength × Frequency
v = λv is called the wave equation.

Audible Frequency

The audible range of human ear is 20 Hz and 20,000HZ, i.e., the human ears can hear only those waves whose frequency lies between 20 Hz and 20,000HZ.

Laws of reflection

There are two basic laws of reflection of sound:
(i) Angle of incidence is equal the angle of reflection.
(ii) The incident wave, the reflected wave and the normal all lie in the same plane.