written 8.2 years ago by | • modified 8.2 years ago |
Mumbai university > FE > SEM 1 > Applied Physics 1
Marks: 5M
Year: May 2013,Dec 2014
written 8.2 years ago by | • modified 8.2 years ago |
Mumbai university > FE > SEM 1 > Applied Physics 1
Marks: 5M
Year: May 2013,Dec 2014
written 8.2 years ago by | • modified 8.2 years ago |
Piezoelectric Effect:-
When a mechanical compression or tension is applied to some crystals like quartz, a potential difference is developed across the crystal which is proportional to the applied pressure. This phenomenon is known as Piezo-electric Effect.
Also if the potential difference is applied across the crystal, a mechanical compression or tension is developed. This is called Inverse Piezo-electric Effect.
Working:-
A variable capacitor (C) and an inductor $(L_2)$ form a tank circuit.
The frequency of the oscillations can be changed by changing the value of capacitance.
When the circuit is closed, the current flows through the circuit and charges the capacitor.
Then the capacitor starts discharging through the inductor, thus the electric energy is stored in the form of electric and magnetic field of capacitor and inductor respectively.
Thus electric oscillations are produced in the tank circuit.
The frequency of this oscillating electricity is given by
$f =\frac{1}{2π\sqrt{L_2 C}}$
With the help of the other electronic components including a transistor, electrical oscillations are produced continuously.
This is fed to the secondary circuit connected to Quartz crystal (Q).
The oscillating electric field is converted to mechanical vibration of crystal owing to the piezoelectric effect.
This vibration produces sound wave of the frequency equal to the frequency of vibration, which is the frequency of electric oscillations.
In this way ultrasonic sound waves can be produced.
Natural frequency of crystal is given by
$f = \frac{k}{2t}\sqrt{\frac{Y}{ρ}}$
When the frequency of electric oscillations is equal to that of natural frequency of the crystal, resonance is achieved and the sound waves of maximum amplitude are produced.