Intensity of Sound and Loudness

Q.

A point source emits sound equally in all directions in a non-absorbing medium. Two points $P$ and $Q$ are at distances of $2m$ and $3m$ respectively from the source. The ratio of the intensities of the waves at $P$ and $Q$ is

1. $9:4$

2. $2:3$

3. $3:2$

4. $4:9$

Q.

A stationary point source of sound emits sound uniformly in all directions in a non-absorbing medium. Two points $P$ and $Q$are at a distance of $4m$ and $9m$ respectively from the source. The ratio of amplitudes of the waves at$P$ and $Q$ is

1. $3/2$

2. $4/9$

3. $2/3$

4. $9/4$

Q. If a bomb explodes on the Moon. After how much time does the sound of the explosion will be heard on Earth?

1. 1800 minutes
2. 3.8 minutes
3. Never be heard
4. 2600 minutes

Q. Which of the following measures are used for minimizing noise pollution?

1. Plant more trees
2. Use soundproof walls
3. Restrict use of crackers
4. All of the above.

Q.

Give scientific reasons:

1. A large number of trees are planted around an airport.

Q.

What is noise pollution? What steps can be taken to prevent it?

Q.

Intensity level of sound whose intensity is${10}^{-8}W{m}^{-2}$ is ______ $dB$.

1. $80dB$

2. $8dB$

3. $4dB$

4. $40dB$

Q. The pleasant sounds are called _________ .

1. music
2. noise
3. pitch
4. loudness

Q. A key of a mechanical piano is struck gently and then struck again but much harder this time. In the second case:

1. Both loudness and pitch will remain unaffected.
2. Sound will be louder but pitch will not be different.
3. Sound will be louder and pitch will also be higher.
4. Sound will be louder but pitch will be lower.

Q. The minimum intensity of audibility of sound is ${10}^{-12}$ watt/$m^2$. If the intensity of sound is ${10}^{-9}$ watt/$m^2$, then calculate the intensity level of this sound in decibels.

Q. A sound of intensity $I$ is greater by $3.0103dB$ from another sound of intensity $10nWc{m}^{-2}$ . The absolute value of intensity of sound level $I$ in ${Wm}^{-2}$ is :

1. $2.5\times {10}^{-4}$
2. $2\times {10}^{-4}$
3. $2.0\times {10}^{-2}$
4. $2.5\times {10}^{-2}$

Q. A source of sound operates at $2.0kHz20W$ emitting sound uniformly in all directions. The speed of sound in air is $340m/s$ and the density of air is $1.2$ $kg/m^3$.
What will be the pressure amplitude at this point?

Q. Two identical speakers emit sound waves of frequency of ${10}^3$ Hz uniformly in all directions. The audio output of each speaker is $9\pi /10$ mW. A point '$P$' is at a distance 3 m from the speaker $S_1$ and 5m from speaker $S_2$. Resultant intensity at $P$ is $I_g$. Match the items in Column I with the items in Column II:

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

Q. The pressure variation that correspond to pain threshold (i.e., the ear can tolerate in loud sound) is about $30Pa$ . velocity of sound in water is $\sqrt{2}\times {10}^{3}m/s$ . The intensity of sound wave produced in water corresponding to loud sound is

1. $1W/m^2$
2. $0.3\times {10}^{-3}W/m^2$
3. ${10}^{3}W/m^2$
4. ${10}^{-12}W/m^2$

Q. Which of the following is true about the speed of sound?

1. It decreases with the density in medium.
2. It is the highest for objects in solid state.
3. It increases from solid to gaseous state.
4. It is independent of the medium of propagation.

Q. Loudness of a sound is measured in_________.

1. metre
2. metre per second
3. hertz
4. decibel

Q. A point source emits sound equally in all directions in a non-absorbing medium. Two points $P$ and $Q$ are at a distance of $2m$ and $3m$ respectively from the source. The ratio of the intensities of the waves at $P$ and $Q$ is -

1. $3:2$
2. $2:3$
3. $9:4$
4. $4:9$

Q. Two sources of sound $S_1$ and $S_2$ vibrate at same frequency and are in phase. The intensity of sound deteced at a point $P$ as shown in the figure is $I_0$. (a) If $\theta$ equals ${45}^o$, what will be the intensity of sound detected at this point, if one of the sources is switched off? (b) What will be the answer of the previous part if $\theta ={60}^o?$

Q. Two sound wave have equal displacement amplitudes, but one has twice the frequency of the other.
What is the ratio of their intensities?

Q. What is the maximum possible sound level in dB of sound waves in air ? Given that density of air is $1.3\times {10}^{5}N/m^2,\nu =332m/s$ and the atmospheric pressure $P=1.01\times {10}^{5}N/m^2$ .

Q. The intensity of sound wave gets reduced by 20% on passing through a slab. The reduction in intensity onpassing through two consecutive slabs is

1. 40%
2. 36%
3. 30%
4. 50%

Q. The intensity of sound is proportional to square of________.

1. wavelength
2. amplitude
3. time period
4. density

Q. You are asked to lower the volume of your television. How will it affect the characteristics of the sound wave?

1. Decrease in amplitude
2. Increase in amplitude
3. Increase in frequency
4. Decrease in frequency

Q.

Two waves of the same pitch have their amplitude in the ratio$3:4$.

What will be the ratio of their intensities?

Q. How much decibals of sound is produced in a normal breathe?

1. 10 dB
2. 40 dB
3. 60 dB
4. 80 dB

Q. Which of the following are the major possible causes for hearing loss?

1. Old age
2. Loud sounds
3. Genetical issues
4. All of the above.

Q. Two sound waves have amplitudes in the ratio 2:5. Ratio of the intensities of the sound waves is:

1. 2:5
2. 5:2
3. 4:25
4. 25:4

Q. A source of sound operates at $2.0kHz20W$ emitting sound uniformly in all directions. The speed of sound in air is $340m/s$ and the density of air is $1.2$ $kg/m^3$.
What will be the displacement amplitude at this point?

Q. (a) The power of sound from the speaker of a radio is $20mW$ . By training the knob of volume control the power of sound is increased to $400mW$ . What is the power increase in dB as compared to original power ? (b) How much more intensive is an $80dB$ sound than a $20dB$ whisper ?