## November 28, 2014

### Senior Inter Physics Important Questions for AP and Telangana

Q: Describe a procedure for measuring the velocity of sound in a
stretched string.
A: A uniform wire is stretched between two rigid supports of a
Sonometer. It is tuned to resonance by adjusting the distance between
the bridges. When the system of a vibrating tuning fork of known
frequency (f) is pressed on the Sonometer board, the paper rider
placed on the wire at its centre is automatically thrown off at
correct resonance.

If 'l' is the distance between the bridges, when resonance occurs,
then l = λ−2 (length of a loop) λ = 2l
The velocity of Sound, V = f λ
V = f × 2l = 2 l f.

Q: What do you understand by "resonance"? How would you use resonance
to determine the velocity of sound in air?
A: Resonance: When the frequency of external periodic force acting on
an oscillator is equal to the natural frequency of the oscillator, it
oscillates with maximum amplitude.
This phenomenon is called resonance. Experiment: When natural
frequency of air column coincides with the frequency of vibrating
tuning fork, the air column would be in resonance with the tuning fork
and the air column
is called resonating air column. Consider a uniform cylindrical tube
which is open at one end and closed at the other end.

The length of air column in the closed tube can be changed by changing
the water level in the tube. When a vibrating tuning fork of known
frequency 'f' Hz is placed close to the opened end of the tube, the
air column in the tube begins to vibrate. Due to reflection of waves
at water surface in the tube and superposition of waves stationary
waves are formed in the air column with node at water surface and
antinode at free end of the tube. The first and second modes of
vibrating air column in resonance with the vibrating tuning fork are
shown in the figure given in the textbook.