Structure of Human Ear | Sound

Speed of ultrasound in sea water, 12.6 Structure of Human Ear v = 1531 m/s How do we hear? We are able to hear with Distance travelled by the ultrasound 2 x depth of the sea = where d is the depth of the sea. speed of sound x time 1531 m/s x 3.42 s = 5236 m 5236 m/2 = 2618 m. Thus, the distance of the seabed from the help of an extremely sensitive device called the ear. It allows us to convert pressure variations in air with audible frequencies into electric signals that travel to the brain via the auditory nerve. The auditory aspect of human ear is discussed below. 2d 2d = d the ship is 2618 m or 2.62 km. Pinna uestion Hammer Anvil 1. A submarine emits a sonar pulse, Stirrup Oval window which from Auditory nerve Cochlea returns an underwater cliff in 1.02 s. If the speed of sound in salt water is 1531 m/s, how far away is the cliff? Tympanic membrane or eardrum Auditory canal Eustachian tube As mentioned earlier, bats search out prey and fly in dark night by emitting and detecting reflections of ultrasonic waves. The high-pitched ultrasonic squeaks of the bat are reflected from the obstacles or prey and returned to bat's ear, as shown in Fig. 12.18. Outer ear Middle Inner ear ear Fig. 12.19: Auditory parts of human ear. The nature of reflections tells the bat where The outer ear is called 'pinna'. It collects the sound from the surroundings. The collected sound passes through the auditory canal. At the end of the auditory canal there is a thin membrane called the ear drum or tympanic membrane. When a compression of the medium reaches the eardrum the the obstacle or prey is and what it is like. Porpoises also use ultrasound for navigation and location of food in the dark. pressure on the outside of the membrane increases and forces the eardrum inward. Similarly, the eardrum moves outward when a rarefaction reaches it. In this way the eardrum vibrates. The vibrations are amplified several times by three bones (the hammer, anvil and stirrup) in the middle ear. 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 turned into electrical signals by the cochlea. These electrical signals are sent to the brain via the auditory nerve, and the brain interprets them as sound. Fig. 12.18: Ultrasound is emitted by a bat and it is reflected back by the prey or an obstacle.