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Use of ultrasonics by bats : Bats have no eyes. But they easily move about without colliding with any object (or obstacle). The reason is that they produce ultrasonic sound as they fly. When this ultrasonic sound comes back after reflection from any object (or obstacle) in their way, they hear it and thus they detect the presence of the object (or obstacle).

1. Ultrasonics – Frequency more than 20000 Hz 

2. Speed of sound in air – 330 m 

3. Infrasonics – Frequency below 20Hz 

4. Sound propagation – Needs material medium

(a) (v) 

(b) (i) 

(c) (iv) 

(d) (ii) 

(e) (iii)

Pitch : 

The pitch of sound depends on the frequency of sound (vibration). It is directly proportional to its frequency. Greater the frequency, higher is the pitch and lesser the frequency, lower is the pitch.

• It is used for medical diagnosis and therapy and also as a surgical tool.

• Bats and porpoises use ultrasound for navigation and to locate food in darkness.

• It is used to detect defective foetus.

• It is used as a tool in the treatment of muscular pain.

• Ultra sonography (is a technique of 3-dimensional photographs with the help of ultrasonic waves) is used to locate the exact position of an eye tumour.

• Ultrasound is generally used to clean spiral tubes,electronic components etc.

• Ultrasound are used to detect cracks and flaws in metal blocks.

The depth of an ocean is determined with the help of SONAR.

Sonar uses ultrasonic waves to detect and locate objects under water.

Ultrasonic waves produced from the transmitter kept in a ship are directed towards the ocean floor.

The ocean floor reflects these waves.

By measuring the time interval t between the generation of the wave and reception of the echo, we calculate the depth of the ocean by using the relation

S = (v x t)/2 Where v is the velocity of ultrasonic waves.

One of the most important applications of the reflection of sound is oceanographic studies. For this purpose, we use a system called the SONAR. The SONAR is abbreviated form of Sound Navigation and Ranging. The SONAR system is used for detecting the presence of unseen under water object, such as submerged submarine, a sunken ship, iceberg and locating them. In Sonar ultrasonic waves are sent in all directions from the ship and are then received on their return after reflection.

Correct Answer is: (b, c, & d)

Correct Answer is: (a) 0.5

We rewrite the given equation as

y = 1/1 +(x - vt)².

For t = 0, this becomes y 

= 1 / (1 + x²), as given.

For t = 2, this becomes 

y = 1 / [1 + (x - 2v)²] 

= 1 / [1 + (x - 1)²].

∴ 2v = 1 or v = 0.5 m/s.

Correct Answer is: (b) V = v, if A = λ/2π 

y = Asin(ωt - kx) 

ω = 2πn,  

k = 2π/λ, 

where n = frequency and λ = wavelength.

Wave velocity = V = nλ = ω/k.

Particle velocity = dy/dt = Aωcos(ωt - kx).

∴ maximum particle velocity = v = Aω.

For V = v₁, ω/k = Aω

or A = 1/k =  λ/2π.

The repetition of sound caused by the reflection of sound waves is called an echo.

• We can hear echo when there is a time gap of 0.1 second in original sound and echo (reflected sound). 

• Echo is produced when sound reflected from a hard surface (i.e., brick wall, mountain etc.) as soft surface tends to absorb sound.

Applications of Ultrasound:

(i) It is used to detect cracks in metal blocks in industries without damaging them.

(ii) It is used in industries to clean ‘hard to reach’ parts of objects such as spiral tubes, odd shaped machines etc. 

(iii) It is used to investigate the internal organs of human body such as liver, gall bladder, kidneys, uterus and heart.

As a sound wave travels through air, the region in which air is at low pressure and low density is called rarefaction.

The greater the vibrating length (or height) of the air column, the less is the frequency of vibration of the column.

The time period (T) and the frequency (f) are inversely proportional to each other T ∝ \(\frac{1}{f}\)

The shrillness of sound is the characteristic property of sound which differentiates the sound between male and female. Usually, the voice of a woman has higher frequency and shriller than the voice of a man.

Correct option is B) decreases

The range of audible sound is from 20 Hz to 20000 Hz or 20 kHz.

1. The sound heard after reflection from a distant obstacle after the original sound has ceased is called an echo, 

2. The conditions for an echo to take place are 

a. The minimum distance between the source of sound and the reflector in air must be 17m. 

b. The size of the reflector must be large enough as compared to the wavelength of sound wave. 

(i) Megaphone : People use horn shaped metal tubes commonly called megaphones while addressing a group of people in fairs or tourist spots. Sound energy is prevented from spreading out by successive reflections from the horn shaped tubes. 

(ii) Hearing aid : Its shape is like a trumpet the narrow end is kept in the ear tube of the person who is hard of hearing. Where as the wider end towards the speaker collects the waves and reflects into the narrow end. This increases the intensity of sound energy hence the person who is hard of hearing can hear clearly. 

ECHO : “The repeated sound heard after reflection from a distant rigid obstacle (such as cliff, a hill side, wall of a building, edge of forest etc.) after the original sound has ceased is called an ECHO.” 

Reverberation : “Due to repeated reflections at the reflecting surface (reflector is less than 17 metres from original sound) the sound gets prolonged, This effect is known as reverberation.” 

Example : 

1. Speaking in a large empty room. 

2. Clapping in tombs like TajMahal.

Two conditions for forming an echo : 

1. The minimum distance between the source of sound and the reflecting body should be 17 metres. 

2. The intensity of sound should be sufficient so that it can be heard after reflection.

1. The phenomenon involved in tuning a radio set to a particular station is called resonance. 

2. Resonance : When the frequency of an externally applied periodic force on a body is equal to its natural frequency, the body readily begins to vibrate with an increased amplitude. This phenomenon is known as resonance. 

3. Loudness is the property by virtue of which a loud sound can be distinguished from a faint one, both having the same pitch and quality. 

4. The loudness of sound is measured in decibel (dB).

Waves in which a disturbance created at one place travels to distant points and keeps travelling unless stopped by an external force are known as travelling or progressive waves. 

Properties of progressive waves are : Amplitude, wavelength, period, double periodicity, frequency and velocity.

Correct option is A) 140

Ultrasonic cleaning is the rapid and complete removal of contaminants from objects by immersing them in a tank of liquid flooded with high frequency sounds waves. These non-audible sound waves create a scrubbing brush action within the fluid.

Bats emit ultrasonic waves and search their food. Ultrasonic waves having higher pitch reflects from prey and reaches ears of the Bat. Nature of reflection indicates to Bat regarding position and type of prey.

Correct option is: (C) 312 m/s

Correct option is: (D) will decrease

Correct option is: (C) Doppler effect

Correct option is C) b, c

Correct option is A) It vibrates air molecule

Correct option is  A) 0

Correct option is C) 1000

Correct option is A) A

Correct option is  B) B