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Music: 

1. The sound that provides a pleasing sensation to the ear. 

2. It is produced by the regular patterns of vibrations. 

Noise: 

1. Sound that is unpleasant to the ear 

2. It is produced by the irregular and nonperiodic vibrations.

True The pitch of sound depends on frequency.

We cannot see the vibrations because the time interval between the two successive vibrations is very less that it hard to observe them.

False Decibel is the unit of the pitch of a sound.

1. We see ripples on the water. 

2. When we strike the rim of the pot, our striking causes vibrations. These vibrations are transferred or moved from the pot to the water. 

Hence, water waves/ripples are seen on the water in the pot.

Frequency is defined as the no.of complete waves that are produced in one second. 

Time period is defined as the time taken by the wave to complete one cycle. 

The relation between frequency and time period is: 

Frequency = 1/ time period

Frequency, f = 1020 Hz 

Velocity, v = 340 m/s 

Wavelength, λ = ? 

= 33.3 cm

Its sound will not be heard outside.

We hear a clearer sound of the water balloon.

(a) The time period of a wave is 2 s. Its frequency is 0.5 S^-1.

(b) The pitch of a stringed instrument is increased by increasing tension in string.

(c) The pitch of a flute is decreased by increasing length of air column.

(d) Smaller the membrane, higher is the pitch.

(e) If a drum is beaten hard, its loudness increases.

(f) A tuning fork produces sound of single frequency.

The noise level is quite low at night. Therefore the sound of the clock appears much clearer at night than in the day.

Hint: Explain how a vibrating body produces sound and how it travels through the air and is heard by us by our ears.

a) Yes, but slightly.

b) Yes, in the second case the sound is feeble.

c) The hand vibrates.

d) Due to the vibrations are transmitted to hand and bell is not properly vibrating so it produces a feeble sound. Once the hand is removed bell rings properly and sound become louder and different. Let us do following activities:

e) Yes, I heard a sound. I felt the vibration.

f) Yes, it produce sound and I found vibrations in the notebook.

g) I heard a sound. The vibrations are found in plate as well as in water.

The loudness of the sound will decrease as the air is removed slowly from the plastic bottle. If the air in the plastic bottle is removed completely, there is vacuum in the bottle. The sound cannot travel through vacuum and we cannot hear the sound of the alarm clock at all.

Correct Answer is: (d) amplitude a/2, frequency 2n and wavelength λ/2

cos²θ = 1/2 (1 + cos 2θ)

∴ y = acos² ( 2πnt - 2πx/λ) = 1/2 a [ 1 + cos { 2π(2n)t - 2πx/(λ/2)}].

Correct option is D) above all

• The two-year-old girl is able to hear the sound. 
• Children can hear sounds of somewhat higher frequencies up to 30 kHz.

• Reflection of sound follows the same laws as the reflection of light when sound is reflected. 
• The directions in which the sound is incident and reflected make equal angles with the normal to the reflecting surface.

The conical openings in horns, megaphones, etc.

will guide the reflected sound waves in forward direction and spreads towards the audience.

Correct option is D) decibel

• Echo is the reflected sound. 
• While it travels back, it gradually loses its energy.
• Hence the echo is weaker than original sound.

Correct option is A) 50 KHz

Echo is the sound heard after reflection from a rigid surface such as a cliff, a hillside, the wall of a building etc.

The answer is (A) 17.2 m

Since sound has to travel an equal distance in going up to the reflecting surface and in coming back from the reflecting surface, therefore it must travel nearly 33/2 = 16.5 m  either way. Thus, to hear the echo clearly in air, the reflecting surface should be at a minimum distance of 16.5 m from the source of sound.

If a person stands at some distance from a wall or a hillside and produces a sharp sound, he hears two distinct sounds: one is original sound heard almost instantaneously and the other one is heard after reflection from the wall or hillside, which is called echo.

The condition for the echo: An echo is heard only if the distance between the person producing the sound and the rigid obstacle is long enough to allow the reflected sound to reach the person at least 0.1 second after the original sound is heard.

For the hearing an echo, the minimum distance between the sound of the source and the reflector should be 17.2 metres.

The minimum distance required between the source and the reflector so as to hear the echo in air is 

2. 17 m 

Correct option is B) Jalatarang

Correct option is C) ii, iv, iii, i

Loudness of a sound depends on the amplitude of the vibration. So to increase loudness of sound by four times, the amplitude of the vibration also to be increased by four times.

Correct Answer is:(a) Aω

The relation between wavelength (A), frequency ( v) and speed of wave (v) is
υ = λv.

1. Wavelength: The distance travelled by the wave during one complete oscillation is called wavelength of the wave.

2. Frequency: The number of oscillations made by the wave in one second is called the frequency of the wave.

3. Time period: The time taken by the wave to complete one oscillation is called the amplitude of the wave.

4. amplitude: The maximum dis-placement of the wave from its mean or equilibrium position is called the amplitude of the wave.

(a) Loudness increases and pitch is higher

Correct option is A) 20

Vocal cords: The two muscular ligaments at the end of the windpipe called vocal cords

When the vocal cord is:

a) Tight and thin: the sound produced is of high frequency or it is of high pitch.

b) Loose and thick: the sound produced is of low frequency or low pitch.

The four sources of sound in a market place are: 

1. Vendors selling eatables or other things. 

2. Shopkeepers selling their things. 

3. Vehicles in the market area, example, auto rickshaw, car, etc. 

4. Machines or generators noise.