# SOUND

Detailed Study:

Brief Revision - Important Question Solving:

Frequently Tested Topics:

• Problems based on ratio of amplitudes

• Factors affecting frequency (in a stretched string, air column, etc.)

• Definition and reason for resonance

• Problems based on speed of sound

Important Past Questions:

• A man playing a flute is able to produce notes of different frequencies. If he closes the holes near his mouth, will the pitch of the note produced increase or decrease? Give a reason.

(2019)

• Two waves of the same pitch have amplitudes in the ratio 1:3. What will be the ratio of their:

i) intensities

ii) frequencies

(2019)

• Define resonant vibrations.

(2019)

• Which characteristic of sound makes it possible to recognize a person by his voice without seeing him?

(2019)

• What do you understand by free vibrations of a body?

(2018)

• Why does the amplitude of a vibrating body continuously decrease during damped vibrations?

(2018)

• The human ear can detect continuous sounds in the frequency range from 20Hz to 20000Hz. Assuming that the speed of sound in air is 330m/s for all frequencies, calculate the wavelengths corresponding to the given extreme frequencies of the audible range.

(2017)

• An enemy plane is at a distance of 300 km from a radar. In how much time will the radar be able to detect the plane? Take velocity of radio waves as 3 x 10^8 m/s.

(2017)

• How is the frequency of a stretched string related to its:

i) length

ii) tension

(2017)

• The ratio of the amplitude of two waves is 3:4. What is the ratio of their:

i) loudness

ii) frequencies

(2010, 2016)

• State two ways by which the frequency of transverse vibrations of a stretched string can be increased.

(2016)

• What is meant by noise pollution? Name one source of sound causing noise pollution.

(2009, 2016)

• Draw a graph between displacement and the time for a body executing free vibrations.

(2015)

• Where can a body execute free vibrations?

(2015)

• ​State the safe limit of sound level in terms of decibel for human hearing.

(2015)

• Name the characteristic of sound in relation to its waveform.

(2012, 2015)

• What are mechanical waves?

(2014)

• Name one property of waves that do not change when the wave passes from one medium to another.

(2014)

• A bucket kept under a running tap is getting filled with water. A person sitting at a distance is able to get an idea when the bucket is about to be filled.

i) What change takes place in the sound to give this idea?

ii) What causes the change in the sound?

(2013)

• A sound made on the surface of a lake takes 3s to reach a boatman. How much time will it take to reach a diver inside the water at the same depth? Velocity of sound in air = 330m/s. Velocity of sound in water = 1450m/s.

(2013)

• Name one factor which affects the frequency of sound emitted due to vibrations in an air column.

(2012)

• Name the unit used for measuring the sound level.

(2012)

• When acoustic resonance takes place, a loud sound is heard. Why does this happen? Explain.

(2011)

• Three musical instruments give out notes at the frequencies listed below. Flute: 400Hz, Guitar: 200Hz, Trumpet: 500Hz. Which one of these has the highest pitch?

(2011)

• With which of the following frequencies does a tuning fork of 256Hz resonate: 288Hz, 314Hz, 333Hz, 512Hz?

(2011)

• State two differences between light waves and sound waves.

(2010)

• An ultrasonic wave is sent from a ship towards the bottom of the sea. It is found that the time interval between the sending and the receiving of the wave is 1.5 seconds. Calculate the depth of the sea if the velocity of sound in sea water is 1400m/s.

(2009)

• A stringed musical instrument, such as the sitar, is provided with a number of wires of different thicknesses. Explain the reason for this.

(2009)

• A radar sends a signal to an aeroplane at a distance 45km away with a speed of 3 x 10^8 m/s. After how long is the signal received back from the aeroplane?

(2008)

• Define the terms:

i) amplitude

ii) frequency

(2007)

• Explain why musical instruments like the guitar are provided with a hollow box.

(2006)

• It is observed that during march past we hear a bass drum distinctly from a distance compared to the side drums.

i) Name the characteristics of sound associated with the above observation.

ii) Give a reason for the above observation.

(2019)