Sound (Physics) PDF

# Sound ## Chapter 10: Sound ### 10.1 Sound Is Produced By A Vibrating Body - Sound is produced by the to and fro motion of a body, also known as vibration. - All sounds are produced by vibrating bodies. - For example, when a tightly stretched band is plucked, it produces sound. - When it stop...

# Sound ## Chapter 10: Sound ### 10.1 Sound Is Produced By A Vibrating Body - Sound is produced by the to and fro motion of a body, also known as vibration. - All sounds are produced by vibrating bodies. - For example, when a tightly stretched band is plucked, it produces sound. - When it stops vibrating, it stops producing sound. - Similarly all musical instruments like veena, sitar and guitar etc. produce musical sounds when their strings are plucked or when they vibrate. ### 10.2 How Is Sound Produced In Humans? - Humans communicate with each other by speaking. - Speaking is the ability to create different types of sounds. - Place your hand on your throat and take out a loud sound. You will be able to feel the vibrations in your throat. - In humans, the sound is produced by a voice box called larynx present at the upper part of the wind pipe in the throat region. - Larynx has two vocal cords (made of ligaments) stretched across it, just like the strings. - There is a slit or gap between the vocal cords for air to pass through. - Sound is produced when the air from the lungs is exhaled out and vibrates the vocal cords. These vibrations in the vocal cord create the sound. ### 10.3 Sound Needs A Medium For Propagation - When the school bell rings at one place in a school, how are you able to hear it in the classroom? - When an object vibrates, the molecules of air in contact with the vibrating object begin to vibrate. - The vibrating air molecules in turn, pass the vibrations to the particles next to them. - This way the vibrations travel in a wave-like pattern in all directions and are known as sound waves. - This is the reason, when the school bell rings at one place in a school, we can hear it in the entire school campus. - When the sound waves reach our ear, our eardrums vibrate and these vibrations are transmitted to the brain. - Our brain interprets these vibrations as sound. - Sound needs a medium to travel. It can travel through solid, liquid or gas. - Sound cannot travel in vacuum. - Sound travels through all directions in a medium. ### 10.4 How Do We Hear Sound? - Sound is carried through a medium in the form of waves. - When these waves reach our ears, we are able to hear sound. - We, humans have ears as the sense organs that allow us to hear or perceive sound. #### Structure and working of human ear - **Outer ear:** It consists of external ear called pinna, ear canal and ear drum. - The part of ear seen outside is called pinna. - It is funnel shaped to receive the sound waves. - From pinna, the sound waves travel through the ear canal to ear drum. - **Ear canal:** It is a passage through which the sound waves travel from pinna to the ear drum. - **Ear drum:** It is a thin elastic membrane stretched tightly at the end of the ear canal. - **Middle ear:** Middle ear has three small bones called: - Malleus - Incus - Stapes. - The sound waves coming from the ear canal make the eardrum vibrate. - Ear drum sends these vibrations to the middle ear. - The sound vibrations from ear drum pass from malleus to incus (stapes). - From stapes, they pass on to the cochlea of the inner ear. - **Inner ear:** Inner ear has cochlea, a coiled tube filled with liquid. - It also has nerve cells which are connected to an auditory nerve that takes the signal to the brain. - The sound vibrations received by cochlea set the fluid in it in motion, which in turn stimulates the nerve cells. - Nerve cells pass the sound signal to the brain through the auditory nerve. - Three semicircular canals present in inner car are for balancing the body and not for hearing. ### 10.5 Basic Terms Related To A Sound Wave - **Amplitude:** It is the maximum displacement of a wave on either side of its mean position. - **Oscillation:** It is one complete to and fro motion of a wave about its mean position. - **Time period:** It is the time taken by a wave to complete one oscillation. It is denoted by ‘T’ and is measured in seconds (s). - **Frequency:** It is the number of oscillations completed by a wave in one second. It is denoted by ‘f’ and is measured in Hertz (Hz). ### 10.6 Audible And Inaudible Sounds - **Audible sounds:** Human ears can hear sounds of frequencies ranging from 20Hz to 20,000 Hz. Sounds within this range are called audible sounds. - **Inaudible sounds:** Sounds of frequency less than 20Hz or greater than 20,000 Hz cannot be detected by human ears. These are called inaudible sounds. - **Ultrasound:** Sounds of frequency more than 20000 Hz are called ultrasounds. We cannot hear the ultrasounds. - The ultrasounds are used for medical purposes like scan during pregnancy to check foetus development. - They are also used in SONAR (Sound Navigation and Ranging), a technique for detecting and finding distance of objects underwater. ### 10.7 Musical Sound And Noise - Some of the sounds we hear are pleasant while some are unpleasant. - We can categorise the sounds as music and noise. #### Sound - **Music:** - Sound is melodious and pleasant to ears. - Sound is harmonius and soothing. - Sound usually has a regular or smooth, periodic pattern. - **Noise:** - Sound is unpleasant and meaningless. - Sound is chaotic and irritating. - Sound has an irregular pattern. ### 10.8 Noise Pollution - Presence of loud, unwanted or unpleasant sounds in the environment is called noise. - Such sounds cause noise pollution in the environment. - There are innumerable sources of noise. - Some of the major sources of noise are as given: - **Outside home:** - Blowing of horn by vehicles - Dog's barking on roads - Bursting of fire crackers - Playing of loudspeakers - **At home:** - Talking loudly and constant ringing of a phone. - Noise of a blender and washing machine. - Creaking of doors and windows. #### Consequences of noise pollution - Damage to ears. Constant loud noise can reduce hearing or cause permanent damage to ears. - Can cause health related problems like lack of sleep, hypertension, and irritation. #### Measures to limit noise pollution - Noise pollution can be controlled to some extent by the following measures: - Installing a silencing device in aircraft engines, transport vehicles and industrial machine/home appliances. - Not playing radio or television too loudly. - Minimize honking while driving. - Planting trees along the roads and around buildings to cut down sound. - Insulating noisy rooms by creating air gaps between walls and windows. #### Hearing Impairment - Hearing impairment means reduced ability to hear. - Total hearing impairment is rare and is usually from birth. - People suffering from total hearing impairment are said to be deaf. - Children suffering from it need special care. - Development of speech is a direct result of hearing. - By learning a sign language, children can learn to communicate effectively. - Partial hearing impairment can be due to a disease, injury or age. - People suffering from it can use a hearing aid on the ear. - Hearing aid helps them to hear properly as it amplifies the small sounds.