物理 WAVE

The lowest frequency that is audiable is about 30 Hz and the highest is about 15 kHz. what is the wavelength in each case? Assume the velocity of sound in air to be 0.33 km/s.

Velocity of sound in air, v
= 0.33 km/s
= 0.33 x 1000 m/s
= 330 m/s

When frequency f = 30 Hz
Wavelength λ
= v/f
= 330/30
= 11 m

When frequency f = 15 kHz = 15 x 1000 Hz = 15000 Hz
Wavelength λ
= v/f
= 330/15000
= 0.022 m

=====
A radar wave is reflected by a jet plane received at 2x10-5 s after it is transmitted. What is the estimated distance between the radar station and the plane?

Radar wave is electromagnetic wave.
Speed of radar wave in air, v = 3 x 108 m/s
Time that the radar wave travels, t = 2 x 10-5 s

Distance that the radar wave travels
= vt
= (3 x 108) x (2 x 10-5)
= 6000 m

Estimated distance between the radar station and the plane
= 6000/2
= 3000 m

=====
With an echo depth sounding equipment, it was found that the echo was received 1.2 sec after the sound impulse was transmitted . calculate the depth of the sea bed below the equipment. assume the speed of sound in sea water to be 1.54 km/s

Speed of sound in sea water, v = 1.54 km/s
Time that the sound travels, t = 1.2 s

Distance that the sound travels
= vt
= 1.54 x 1.2
= 1.848 km

Depth of the sea bed
= 1.848/2
= 0.924 km (or 924 m)
=