Free Download NCERT Solutions for Class 9 Science Chapter 12 Sound in PDF form. Solutions of other subjects are also available free to download. 9 Science NCERT Solutions all chapter are given in PDF form.
NCERT Solutions for Class 9 Science Chapter 12
Class 9 Science – Physics – Sound
Important questions with answers for practice
- Question 1:
Chandigarh radio station broadcast at 1200 kHz. At what metre Chandigarh station would be tuned in your transistor?
- Answer 1:
- Question 2:
A bat emits unit ultrasonic sound of frequency 100 kHz in air. If this sound meets a water surface, what is the wavelength of (a) the reflected sound wave (b) the transmitted sound wave. Given speed of sound in air = 340 m/s and in water = 1486 m/s.
- Answer 2:
(a)3.4 x 10-³ m (b) 1.486 x 10-²
- Question 3:
A hospital uses an ultrasonic scanner to locate tumour in a tissue. What is the wavelength of sound in a tissue in which the speed of sound is 1.7 km/s? The operating frequency of the scanner is 4.2 MHz .
- Answer 3:
- Question 4:
An engine is approaching a hill at constant speed when it is at a distance of 0.9 km, if blows a whistle, whose echo is heard by the driver after 5 s. if the speed of sound is 340 m/s, calculate the speed of the engine.
- Answer 4:
- Question 5:
A person standing between two vertical cliffs and 680 m away from the nearest cliff, shouted . he heard the first echo after 4 s and the second echo 3 s later, calculate (a) the speed of sound in air and (b) distance from the two cliffs.
- Answer 5:
(a) 340 m/s (b) 1870 m
- Question 6:
A sonar emits pulses on the surface of water which are detected after reflection from its bottom at a depth of 1534 m. if the time interval between the emission and detection of the pulse is 2 s, find the speed of sound in water.
- Answer 6:
- Question 7:
Distinguish between music and noise?
- Answer 7:
- 1. It has a pleasant effect on the ear.
- 2. It consists of a series of sound impulses which follow one another regularly.
- 3. The frequency of musical sound is high
- 4. There are no sudden changes in amplitude (loudness) of the wave constituting a musical sound.
- 1. It has an unpleasant effect on the ear.
- 2. The sound impulses do not follow one another regularly.
- 3. The frequency of noise is low.
- 4. There are usually sudden changes in amplitude (loudness) of the wave forming a noise.
- Question 8:
What is SONAR? How is it used to detect an underwater object and measure its distance?
- Answer 8:
It is an acronym which means Sound Navigation And Ranging.
Sonar is a device which measures the distance, direction and speed of objects lying under water ultrasonic waves.
The above method of finding the distance of an object is called echo-ranging as it is based on echo principle. The sonar technique is used to:
(i) Determine depth of the sea , called echo depth ranging. When used for purpose , it is called fathometer as it directly fathoms the depth of the sea.
(ii) Locate underwater hills, valleys, icebergs, submarines and sunken ships.
(iii) To locate the position of other ships or submarines. Ship to ship communication also uses ultrasonic waves. The advantage of using ultrasonic waves is that these waves cannot be heard without the aid of special instruments.