Question 13 Marks
(i) (a) What is an echo?
(b) State two conditions necessary for the formation of an echo.
(ii) What is sonar? State its principle. How is it used to find the depth of sea?
(iii) How do the following use echoes?
(a) army, (b) geologist, (c) medical sciences
(b) State two conditions necessary for the formation of an echo.
(ii) What is sonar? State its principle. How is it used to find the depth of sea?
(iii) How do the following use echoes?
(a) army, (b) geologist, (c) medical sciences
Answer
View full question & answer→(i) (a) Echo is the sound heard after reflection from a distant obstacle, after the original sound has died off.
(b) Conditions necessary for echo formation: (i) The minimum distance between the source of sound and reflecting object/obstacle should be 17 metres.
The size of the obstacle must be larger than the wavelength of sound.
(ii) Sonar stands for Sound Navigation and Ranging and the technique used to measure distances by using ultrasonic waves. To find the depth of an ocean, ultrasonic waves from the ship is sent towards the bottom of the ocean. These waves are then received by a suitable receiver, after reflection from the ocean floor. The distance of the bottom of ocean is calculated by measuring the time interval between the instant when waves are sent and the instant when reflected waves are received. Using the value of velocity of sound in water, the depth of ocean floor can be calculated.
(iii) (a) Army uses echoes to locate the gun positions of the enemy.
(b) Geologists use echoes for mineral prospecting.
(c) Echoes produced by ultrasonic waves are used for imaging internal human organs, such as prostate gland, womb, liver, gall bladder. Such imaging is called ultrasonography. Similarly, echo cardiography is used to take the image of heart.
(b) Conditions necessary for echo formation: (i) The minimum distance between the source of sound and reflecting object/obstacle should be 17 metres.
The size of the obstacle must be larger than the wavelength of sound.
(ii) Sonar stands for Sound Navigation and Ranging and the technique used to measure distances by using ultrasonic waves. To find the depth of an ocean, ultrasonic waves from the ship is sent towards the bottom of the ocean. These waves are then received by a suitable receiver, after reflection from the ocean floor. The distance of the bottom of ocean is calculated by measuring the time interval between the instant when waves are sent and the instant when reflected waves are received. Using the value of velocity of sound in water, the depth of ocean floor can be calculated.
(iii) (a) Army uses echoes to locate the gun positions of the enemy.
(b) Geologists use echoes for mineral prospecting.
(c) Echoes produced by ultrasonic waves are used for imaging internal human organs, such as prostate gland, womb, liver, gall bladder. Such imaging is called ultrasonography. Similarly, echo cardiography is used to take the image of heart.