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1. sound waves 

2. medium 

3. From 20 Hz to 20 KHz 

4. below 20 Hz 

5. ultrasonic waves 

6. 1.65 cm to 1.65 m 

7. longitudinal 

8. V = \(\frac{λ}{T}\)

9. V = nλ 

10. V_s > V_L > V_G

11. density 

12. elastic modulus 

13. rainy seasons 

14. 0.61 m/s 

15. the angle of reflection 

16. decreased 

17. parabolic surface 

18. elliptical 

19. echo

20. 0.1 second 

21. sound waves 

22. echo 

23. relative motion 

24. n’ = (\(\frac{V + V_L}{V-V_S}\) )n

 25. velocities 

26. (\(\frac{V + V_L}{V}\))n 

27. more, actual 

28. [V – W] 

29. away from, stationary 

30. stationary

1. Wave 

2. South to north 

3. 500 Hz 

4. 2067-3 Hz

It both the trains are approaching each other. 

The apparent frequency, \(n' = (\frac{v + v_0}{v - v_s})\,n\)

\(n' = (\frac{330 + 15}{330 - 30}) \times 516\)

\(n = \frac{345}{300} \times 516 = 1.15 \times 516\)

\(n'\) = 593.4 Hz

Sound waves travel faster in solids with greatest speed. Because the coefficient of elasticity of solids is much greater than coefficient of elasticity of liquids and gases.

1. When source (S) and listener (L) both are at rest. 

2. When S and L move in such a way that distance between them remains constant.

Velocity of radio waves v = 3 × 10⁸ m/s 

Wavelength of radio waves λ = 219.3 m 

∴ Frequency of radio waves v = \(\frac{v}{λ}\)

v = \(\frac{3 \times 10^8}{219.3}\)

 = 0.013679 x 10⁸

= 13679 x 10²

= 1.36 79 × 10³Hz

Frequency v = 1.3679 KHz

(c) stationary wave

Wave velocity = Frequency × Wavelength

v = vλ

The minimum distance needed for an echo is 17.2 metre.

In longitudinal wave, the particles of the medium vibrate along the direction of the wave.

By touching a ringing bell or a musical instrument while it is producing music, we conclude that sound is produced by vibrations.

• We hear the sound even when we close our ears but its magnitude and frequency is very less due to the obstruction of our hands. 
• It also depends upon the frequency and loudness of the sound

Audible waves: These are sound waves with a frequency ranging between 20 Hz and 20,000 Hz.

Wave velocity v = \(\frac {λ}{T}\)

(or) λ = vT

The audible range of frequency is from 20 Hz to 20 KHz.

The velocity with the particles of the medium vibrate in order to transfer the energy in the form of a wave is called particle velocity.

(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.

(b) If both the assertion and the reason are true but the reason is not the correct explanation of the assertion.

The velocity with which the wave travels through the medium is called wave velocity. In other words, the distance travelled by a sound wave in unit time is called the velocity of a sound wave.

∴ velocity = \(\frac{Distance}{Timetaken}\)

Wave velocity is defined as the distance travelled per second by a sound wave. Since, 

Frequency (n) = 1/T, 

V = \(\frac{λ}{T}\) can be written as V = nλ.

The velocity of sound in a gas is inversely proportional to the square root of the density of the gas. Hence, the velocity decreases as the density of the gas increases.

V ∝ \(\sqrt{\frac{1}{d}}\)

The velocity of sound in a gas is directly proportional to the square root of its temperature. The velocity of sound in a gas increases with the increase in temperature. 

V ∝ √T . 

Velocity at temperature T is given by the following equation:

V_T = (V₀ + 0.61T) ms²

• Effect of density 
• Effect of temperature 
• Effect of humidity

Effect of density:

The velocity of sound in a gas is inversely proportional to the square root of the density of the gas. Hence, the velocity decreases as the density of the gas increases.

v ∝ \(\sqrt{\frac{1}{d}}\)

Effect of temperature: 

(i) The velocity of sound in a gas is directly proportional to the square root of its temperature. 

(ii) The velocity of sound in gas increases with the increase in temperature, v ∝ √T 

Velocity at temperature T is given by the following equation:

v_T = (v₀ + 0.61 T) ms^-1

Here, v₀ is the velocity of sound in the gas at 0° C. For air, 

v₀ = 331 ms^-1

Hence, the velocity of sound changes by 0.61 ms^-1 when the temperature changes by one – degree celsius. 

Effect of relative humidity: When humidity increases, the speed of sound increases. That is why we can hear sound from long distances clearly during rainy seasons.

(b) reflection at the boundary of a denser medium

The animals are dogs, bats and dolphins.

(a) Ultrasonic Vibration: The vibrations whose frequencies are greater than 20000 Hz are called ultrasonic vibrations. 

(b) 

(i) They are used in SONAR to measure the depth of the sea (or ocean) and to locate underwater objects.

(ii) It is used for scanning and imaging the position and growth of a foetus and presence of stones in the gall bladder and kidney. 

(iii) It is used for homogenising milk in milk plants where fresh milk is agitated with the desired quantity of fat and powdered milk to obtain toned milk.

(c) Mosquito, Dogs and Bats are the three animals that can hear ultrasonic vibrations.

(c) 330 × √2 ms^-1

As there is no effect of change in pressure on the velocity of sound in air, and v ∝ √T therefore, when the temperature is doubled, so the velocity becomes 330√2 m/s.

Frequency of sound = \(\frac{velocity \, of\, sound}{wavelength\, of\, sound}\)

\(n\) = \(\frac{v}{λ}\) = \(\frac{331}{0.20}\)

n = 1655 HZ.

Speed of sound wave v = 400 m/s 

Frequency of sound wave n = 200 Hz 

∴ Wavelength sound wave λ = \(\frac{v}{n}\) = \(\frac{400}{200}\) = 2 m 

∴ Wavelength = 2 m

(b) Longitudinal waves

(b) Light: Since the velocity of light (C = 3 × 10⁸ m/s) is greater than the velocity of sound, light wave has a longer wavelength.

(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.

(b) If both the assertion and the reason are true but the reason is not the correct explanation of the assertion.

(c) Echo sound

One of the famous whispering galleries is in St. Paul’s cathedral church in London. It is built with elliptically shaped walls. When a person is talking at one focus, his voice can be heard distinctly at the other focus. It is due to the multiple reflections of sound waves from the curved walls.

(d) amplitude

(d) pressure

(b) less than 17.2 m

(d) none of these

When sound waves are reflected from a plane surface, the reflected waves travel in a direction, according to the law of reflection. The intensity of the reflected wave is neither decreased nor increased.

(i) – (C) 

(ii) – (E) 

(iii) – (A) 

(iv) – (D)

An electromagnetic wave is emitted by a source attached to a police car. The wave is reflected by a moving vehicle, which acts as a moving source. There is a shift in the frequency of the reflected wave. From the frequency shift, the speed of the car can be determined. This helps to track the over speeding vehicles.

Correct answer is (b) 20 kHz

(a) 330 ms^-1

Pressure has no effect on the velocity of sound in the gas. So velocity of sound remains unchanged.

Correct answer is (c) gaseous

(b) decreases

(b) equal to angle of incidence

The intensity of sound is directly proportional to the square of the amplitude of vibration. I ∝ A² since, the amplitude of vibration of air molecules (empty vessel) is greater than liquid molecules (filled vessel), therefore empty vessel produces a louder sound than the filled vessel.