ISLAMABAD ACADEMY PHYSICS FOR 10TH CLASS (UNIT # 13)

Transcription

1 PHYSICS FOR 10TH CLASS (UNIT # 13) SHORT QUESTIONS How sound is produced? It is produced from a vibrating body which transfers in air from one place to other in the form of compression waves. A medium is necessary for the traveling of sound. Give some examples of production of sound. i) Strike a spoon on a pan. A particular sound is produced. You can feel its vibration by touching it with your finger. ii) If we strike a tuning fork on a rubber pad, a sound is heard and the prongs of the tuning for start vibrating. Name the three parts of ear? Outer ear, Middle earn, Inner ear Name the three bones in middle ear? There are three movable bones in middle ear. i.e. hammer, anvil and stirrup In which ear cochlea is present? Inner ear. Which nerve carry sound waves to brain? Auditory Nerve. Define loudness of sound? It is a characteristic of sound by which loud and faint sounds can be distinguished On which factors loudness of sound depends? i) Amplitude of vibrating body ii) Area of vibrating body iii) Distance from vibrating body Define intensity of sound Sound energy flowing per second through a unit area held perpendicular to the direction of sound waves is called the intensity of sound. Define pitch of sound? The characteristic of sound by which a shrill sound and grave sound can be distinguished. How voice becomes shrill and grave? Higher pitch shows lower frequency. Frequencies of voices of ladies and children are greater and their voice is shrill. The frequencies of old men are lesser and their sound is grave. Define quality of sound? The characteristics of sound by which two sounds of same loudness and pitch can be distinguished. Differentiate between noise and music? The sound, which has pleasant effect on our ears, is called Music. The sound, which produces jarring effect on our ears, is called noise. What is audible frequency range? As name indicates, it is a range of sound s frequency, which a person can hear. A human ear can hear a sound only if its frequency lies between 20 and 20,000 hertz (Hz). If the frequency of sound is less or 1

2 greater than this range then that sound is in-audible and could not be heard. This range can be slightly differs in different persons. What are ultrasonic s? We know that human ear can hear a sound of frequency between 20 and 20,000 hertz. The sounds of higher frequencies are utilized in many useful ways. These sounds are called ultrasonic s. Define decibel scale? Bel, is the large unit of intensity level of a sound. A smaller unit is called decibel. It is denoted by (db). While 1 Bel is equal to 10dB. Define resonance The Phenomenon in which there is remarkable increase in the amplitude and hence the loudness of sound when the frequency of air column becomes equal to that of the tuning fork, is called resonance. What is tuning fork? It is device used to produce particular sound in laboratories and schools. The sounds produced by explosions going on the sun are not heard on the earth why? Sound waves need a medium to travel. As there is no material medium between earth and sun, therefore we could not hear the sound of these explosions. What are characteristics of musical sound? Frequency and amplitude of musical sound does not change suddenly and regularly. They remain constant most of the time. What are infra Sonics The sound waves whose frequency is less than 20 Hz, which cannot be heard by human ear, are called infra Sonics. Why we cannot hear sound produced by simple pendulum Because its frequency is less than 20 Hz. While human can hear only those sounds, whose frequency lies between Hz. How can we measure the depth of the ocean? An ultrasonic pulse is sent down towards the ocean bed from the bottom of ship. This pulse after reflection from the ocean bed, reaches the ship where it is detected. The time taken by the ultrasonic pulse in traveling from ship to the ocean bed and back to the ship is measure. Using this time and speed of sound in water the depth of ocean can be determined. How can we search the oil and gas resources beneath the earth? These resources can be searched by using the ultrasonic s. How can you distinguish between two sound of same loudness and pitch played by guitar and flute? Quality of sound characteristics, is used to distinguish such sound. How cracks in the interior of the moving parts of high speed heavy machines can be detected? A powerful beam of ultrasonic is made to pass through these defective parts. While passing these waves are reflected by the surface of these cracks and flows. The comparison of the ultrasonic s waves reflected from the cracks and from the other surfaced of these parts can give a clue of the existence of the cracks. What type of waves are produce by vibrating tuning fork? Compressional Waves. How ultra sonic waves are used in diagnostic purposes? 2

3 Ultrasonic waves are made to enter the human body. These waves are reflected differently by different organs, tissues, benign or malignant tumors. Reflected ultrasonics waves are then amplified and fed to a monitor, which forms an image of the internal organs of body on its screen. This image helps indetecting the defects. What is Weber Fechner s law? Loudness of sound is always directly proportional to Area of vibrating body. LONG QUESTIONS >>Question: How sound is produced? Give Examples Sound is a form of energy. It is produced from a vibrating body which transfers in air from one place to other in the form of compressional waves. A medium is necessary for the traveling of sound. For example: i) Strike a spoon on a pan. A particular sound is produced. You can feel its vibration by touching it with your finger. ii) If we strike a tuning fork on a rubber pad, a sound is heard and the prongs of the tuning for start vibrating. >>Question: What is the nature of sound? How sound waves propagate? We know that sound is produced due to vibrations of bodies. When a body vibrates its start moving to and fro about its mean position. Due to this motion compressional waves are produced. These waves are called sound waves. They can travel from one place to other. Propagation of sound Experiment: *** Draw figure from book Place a bell jar on vacuum pump. Suspend an electric bell in it with the help of two wires. Fix a cork in the mouth of bell jar. On ringing the bell sound can be heard. Now start expelling the air form jar by vacuum pump. The sound becomes faint and faint. At last sound become hardly heard. By this experiment it has proved that medium is necessary for propagation of sound waves. >>Question: Write a note on detection of sound? How sound is heard? We hear the sound by ear. Ear has three parts: - Outer Ear: This is horn like part, which we can see outside. This ear collects the sound waves and directs them to eardrum. Eardrum separates the outer ear from middle ear. 3

4 Middle Ear: Eardrum passes the collected vibrations of sound to middle ear. This ear is small irregular cavity. It consists of three moveable bones called hammer, anvil and stirrup. Inner Ear: Vibrations of the eardrum are passed to the inner ear. This ear has complicated structure. It plays an important role in hearing. It has a part cochlea. Then these sounds waves converted into messages and send to brain by auditory nerve. Then we recognize the sound. >>Question: Write down the characteristics of sound? There are following characteristics of sound: - i) Loudness: It is a characteristic of sound by which loud and faint sounds can be distinguished. Loudness of sound depends upon following factors: a. Amplitude of Vibrating Body: If amplitude of vibrating body is large then loud sound will be produced and if amplitude is small then faint sound will be produced e.g. when we strike the drum forcefully loud sound will be produced due to large amplitude. b. Area of Vibrating Body: If the area of vibrating body is larger then loud sound will produced and if the area of vibrating body is small then faint sound will produced e.g. sound produced by larger drum will be loud then a small drum. c. Distance from vibrating body: Loudness of sound also depends upon the distance between producer and listener. Greater distance between them result in faint sound. Less distance between them results in loud sound. ii) Intensity of Sound: Sound energy flowing per second through a unit area held perpendicular to the direction of sound waves is called the intensity of sound. It is physical quantity and does not depend on the condition of ear. iii) Pitch of Sound: The characteristic of sound by which a shrill sound and grave sound can be distinguished. Higher pitch shows lower frequency. Frequencies of voices of ladies and children are greater and their voice is shrill. The frequencies of old men are lesser and their sound is grave. iv) Quality of Sound: The characteristics of sound by which two sounds of same loudness and pitch can be distinguished. v) Noise & Music: The sound, which has pleasant effect on our ears, is called Music. The sound, which produces jarring effect on our ears, is called noise. 4

5 >>Question: What are uses of ultra sonics? i) In medical fields ultrasonic waves are used to diagnose and treat many ailments. ii) They help in the formation of image of internal organs. iii) They help to find the sex of baby before birth in the womb of mother. iv) They help to remove blood clots in arteries. v) They help to find the depth of ocean and rivers. vi) They help to destroy germs and bacteria present in liquids. vii) The resources of oil and gas beneath the Earth are searched by using ultrasonics. viii) Kidney stones can be crushed and removed out through urine without surgery. 5