The Loudness

Q.

The sound level at a point is increased by 30dB. By what factor is the pressure amplitude increased?

1. 16 times

2. 10 times

3. 8 times

4. 32 times

Q. An 𝑋-ray tube produces a continuous spectrum of radiation with its short wavelength end at $0.45\stackrel{\circ }{A}$. What is the maximum energy of a photon in the radiation?

B) An X-ray tube produces a continuous spectrum of radiation with its short wavelength end at $0.45\stackrel{\circ }{A}$ with maximum energy of a photon in the radiation being $27.6\text{keV}$. Guess what order of accelerating voltage (for electrons) is required in such a tube?

Q. Three photo diodes $D_1,D_2$ and $D_3$ are made of semiconductors having band gaps of $2.5eV,2eV$ and $3eV$, respectively. Which ones will be able to detect light of wavelength $6000\stackrel{0}{A}$ ?

$\text{Formula Used}:E=\frac{hc}{\lambda }$

Q.

You live on a busy street, but as a music lover, you want to reduce the traffic noise. If you install special sound-reflecting windows that reduce the sound intensity level (in dB) by 30 dB, by what fraction have you lowered the sound intensity $\left(in\frac{w}{m^2}\right)$?

1. 

2. 

3. 

4. 

Q.

The sound level at a point is increased by 30 dB. By what factor is the pressure amplitude increased?

1. In 30

2. 32

3. 30

4. 3

Q.

If the pressure amplitude in a sound wave is tripled, then the intensity of

sound is increased by a factor of

1. 3

2. 9

3. 

4. 6

Q. Consider a $20W$ bulb emitting light of wavelength $5000\stackrel{o}{A}$ and shining on a metal surface kept at a distance $2m$. Assume that the metal surface has work function of $2eV$ and that each atom on the metal surface can be treated as a circular disk of radius $1.5\stackrel{o}{A}$.

A) Estimate no. of photons emitted by the bulb per second. [Assume no other losses]

B) Will there be photoelectric emission?

C) How much time would be required by the atomic disk to receive energy equal to work function $\left(2eV\right)$?

D) How many photons would atomic disk receive within time duration $11.37s$?

E) Can you explain how photoelectric effect was observed instantaneously?

Q. Which parameter has a more direct influence on the loudness of a sound wave?

1. Displacement Amplitude
2. Pressure amplitude

Q.

Sound with intensity larger than $120dB$appears painful to a person. A small speaker delivers $2·0W$ of audio output. How close can the person get to the speaker without hurting his ears?

Q. When radiation of wavelength $\lambda$ is used to illuminate a metallic surface, the stopping potential is $\text{V}$. When the same surface is illuminated with radiation of wavelength $3\lambda$, the stopping potential is $\frac{\text{V}}{4}$. If the threshold wavelength for the metallic surface is $n\lambda .$ The value of $n$ will be

Q.

Sound with intensity larger than 120 dB appears painful to a person. A small speaker delivers 2.0 W of audio output. How close can the person get to the speaker without hurting his ears ?

Q. Ultraviolet light of wavelength $2271\stackrel{\circ }{A}$ from a $100W$ mercury source irradiates a photocell made of molybdenum metal. If the stopping potential is $-1.3V$, estimate the work function of the metal. How would the photocell respond to a high intensity $(\sim {10}^{5}W/m^2)$ red light of wavelength $6328\stackrel{\circ }{A}$ produced by a He-Ne laser?

Q. Light of wavelength 488 𝑛𝑚 is produced by an argon laser which is used in the photoelectric effect. When light from this spectral line is incident on the emitter, the stopping (cut - off) potential of photoelectrons is $0.38V$. Find the work function of the material from which the emitter is made.

Q.

If a sound absorber attenuates the sound level by $20dB$. The factor by which the intensity decreases is

1. $1000$

2. $10000$

3. $10$

4. $100$

Q. Name the unit used to measure the sound level:

1. decibel
2. joule
3. watt
4. Hz

Q. If the sound level in a room is increased from 50 dB to 60 dB, by what factor is the pressure amplitude increased?

1. None of these

2. 10

3. 2

4. 

Q. If the ratio of two sound intensities is $1:9$, the ratio of their amplitude of sound wave will be:

1. $\frac{1}{3}$
2. $\frac{1}{4}$
3. $\frac{1}{8}$
4. $\frac{1}{18}$

Q. Sound with intensity larger than 120 dB appears painful to a person. A small speaker delivers 2.0 W of audio output. How close can the person get to the speaker without hurting his ears?

1. 40 cm

2. 80 cm

3. 120 cm

4. 10 cm

Q. When excess pressure of $2\times {10}^{5}Pa$ is applied on water, the fractional change in its volume is approximately ${10}^{-n}$. Take speed of sound in water as $1400m/s$ and density of water as $1000kg/m^3$, then $n$ is

1. 1
2. 2
3. 3
4. 4

Q. Spherical sound waves are emitted uniformly in all directions from a point source. The variation in sound level SL as a function of distance ‘r’ from the source can be written as
Where a and b are positive constants.

1. 
2. 
3. 
4. 

Q. Spherical sound waves are emitted uniformly in all directions from a point source. The variation in sound level SL as a function of distance ‘r’ from the source can be written as
Where a and b are positive constants.

1. $SL=-blog{r}^a$
2. $SL=a-b(logr{)}^2$
3. $SL=a-blogr$
4. $SL=\frac{a-b}{r^2}$

Q. A tube of certain diameter '$d$' and of length $48cm$ is open at both ends. Its fundamental frequency of resonance is found to be $320Hz$ and the speed of sound in air is $320m/s$. Estimate the diameter of the tube. If one end of the tube is closed then, calculate the lowest frequency of resonance for the tube.

Q. If the pressure amplitude of any sound wave is increased by 100 %, then what is the % increase in its intensity ?

1. 100 %
2. 300 %
3. 200 %
4. 150 %

Q. Sound with intensity larger than 120 dB appears painful to a person. A small speaker delivers 2.0 W of audio output. How close can the person get to the speaker without hurting his ears?

1. 40 cm

2. 120 cm

3. 10 cm

4. 80 cm

Q. The anode voltage of a photocell is kept fixed. The wavelength $\lambda$ of the light falling on the cathode is gradually changed. The plate current $I$ of the photocell varies as follows

1. 
2. 
3. 
4. 

Q. A musical tone that is lower in pitch is lower in frequency{f}.

1. False.
2. Data insufficient.
3. True.
4. Ambiguous.

Q. If the amplitude of a sound wave is tripled,
By what factors will the intensity increase?

Q. Due to a point isotropic sonic source, loudness at a point is L = 60 dB. If density of air is $\rho =\left(\frac{15}{11}\right)kg/m^3$ and velocity of sound in air is v = 330 m/s, the pressure oscillation amplitude at the point of observation is $[I_0={10}^{-12}W/m^2]$

1. 
2. 
3. 
4. 

Q. Figure shows a parabolic graph between T and I/V for a mixture of a gas undergiong an adiabatic process. What is the ratio of $V_{rms}$ of molecules and speed of sound in mixture:

1. $\sqrt{3/2}$
2. $\sqrt{2}$
3. $\sqrt{3}$
4. $\sqrt{2/3}$

Q. If the bulk modulus of water is $2100MPa$, what is the speed of sound in water?

1. $1450m{s}^{-1}$
2. $2100m{s}^{-1}$
3. $1400m{s}^{-1}$
4. $1200m{s}^{-1}$