# physics numericals for class 9 sound with answers

Assignments NCERT Solutions

Given below are the physics numericals for class 9 sound with answers
a) Concepts questions
b) Calculation problems

Question 1.A stone is dropped from a 50 m tall building into a pond. When is sound of splash heard at the top? (g=10m/s2 , speed of sound in air= 340m/s)?
Question 2.Define one hertz?
Question 3.Audible frequency range of a human ear is 20 hertz to 20000hertz. Express it in terms of time period?
Question 4.Derive the relationship between wavelength, frequency and speed of sound?
Question 5.Define wavelength?
Question 6.Draw a graph showing density and pressure variations with respect to distance for a disturbance produced by sound wave? Mark the position of compression and rarefaction on this curve/graph. Name the regions of maximum and minimum change in pressure respectively?
Question 7. Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a darkroom?
Question 8.Explain with the help of bell jar experiment that sound cannot travel in vaccum?
Question 9.What is a transverse wave?
Question 10. A radar signal is received 2*10-5   sec. After it was sent and reflected by an aeroplane. How far is the aeroplane if speed of waves is 3*108 m/s?

Question 11.Give two practical applications of reflection of sound waves?
Question 12.Briefly mention three uses of ultrasound in the field of medicine?
Question 13.Distinguish between transverse waves and longitudinal waves?
Question 14.How temperature affects the velocity of sound?
Question 15.Guess which sound has a higher pitch; guitar or car horn?
Question 16.When vertically upward jerk is given to a string, transverse waves are formed? Give three reasons?
Question 17.A tuning fork having frequency 312Hz emits a wave which has a wavelength of 1.10m. Calculate the speed of sound?
Question 18.Which wave property determines pitch?
Question 19.Why do we hear the sound produced by a humming bees while sound of vibrations of a simple pendulum is not heard?
Question 20.In tank, 10 ripples are produced in one sec. If the distance between a crest and trough is 10cm, find?
a) Wavelength
b) Frequency
c) Velocity of the wave?
Question 21.A wave is moving in air with a velocity of 340m/s. Calculate the wavelength if its frequency is 512Hz?.
Question 22.Find the distance of cloud from you when you hear a thunder 3 sec after the lightning is seen. (given the speed of light= 3*108 m/s, speed of sound= 330m/s)? Why is lightning seen a few seconds before the thunder is heard during a thunderstorm?
Question 23.Why do we hear more clearly in a room with curtains than in a room without curtains? Explain in brief?
Question 24.Explain giving reason the purpose of using curved ceilings in cinema halls?