Test: Ultrasound And Human Ear - Class 9 MCQ

Another popular use for ultrasonics is in ships, both for navigation and for locating objects underwater. Sound travels faster through water than through air, which is very helpful because light hardly travels through water at all. Most people know that whales can use low-frequency sound to communicate across entire oceans. Submarinesuse a similar trick with a type of navigation called sonar (sound navigation and ranging), which is a bit like an underwater equivalent of radar.

Speed of sound in air, v = 342 ms^-1

Time taken for hearing the echo, t = 3 s 

Distance  travelled by the sound = vt 

= 342 * 3 

= 1026 m

In 3 s, sound has to travel twice the distance between the the cliff and the person. 

Hence the distance between the cliff and the person is given by, d=  1730 m/2 = 865 m

The middle ear transmits the amplified pressure variations received from the sound wave to the inner ear. In the inner ear, the pressure variations are turnedinto electrical signals by the cochlea. These electrical signals are sent to the brain via the auditory nerve, and the brain interprets them as sound.

The pressure from sound waves makes the eardrum vibrate. The vibrations are transmitted further into the ear via three bones in the middle ear: the hammer(malleus), the anvil (incus) and the stirrup (stapes).

Human beings can normally hear sounds with a frequency between about 20 Hzand 20,000 Hz. Sounds with frequencies below 20 hertz are called infrasound.Infrasound is too low-pitched for humans to hear. Sounds with frequencies above 20,000 hertz are called ultrasound.

 The technique used by bats to find their way or to locate food is echo-location. 

When bats detect ultrasonic waves which after touching the prey comes back to bats ear which tell them how far their prey is and how it looks like. Similarly people detect ultrasonic waves to know the distance. the waves touch the building and comes back which tells us how far it is.

Its all because Children below 5-6 years and some small animals like cat, dog, rat etc.. have innovation Sound hearing that's why they can hear sound upto 25Khz.

2 D = velocity X time
D = (velocity X time) / 2 = 1450 X 4 / 2 = 2900 m = 2.9 km