Revisiting Waves

Q. A microphone of cross-sectional area 0.80 $c{m}^2$ is placed in front of a small speaker emitting 3.0 W of sound output. If the distance between the microphone and the speaker is 2.0 m, how much energy falls on the microphone in 5.0 s?

1. 

2. 

3. 

4. 

Q.

What is the wavelength of ultrasonic waves in air?

Q.

The equation of a simple harmonic progressive wave is given by
y = 8sin (0.628x – 12.56t)
where x and y are in cm and t is in second.
Find the phase difference in degrees between two particles at a distance of 2.0cm apart at any instant.

1. 57

2. 45

3. 64

4. 72

Q.

Two passenger trains moving with a speed of 108 km/hour cross each other.

One of them blows a whistle whose frequency is 750 Hz. If sound speed is

330 m/s, then passengers sitting in the other train, after trains cross each

other will hear sound whose frequency will be

1. 900 Hz

2. 625 Hz

3. 750 Hz

4. 800 Hz

Q.

A wave of wavelength 0.60 cm is produced in air and it travels at a speed of 300 m s${}^{-1}$. Will it be audible?

1. Yes

2. No

3. Data insufficient

Q. Two monochromatic light waves of amplitudes $A$ and $2A$ interfering at a point, have a phase differences of ${60}^{\circ }$. The intensity of the resultant wave at that point will be proportional to

1. $3A^2$
2. $5A^2$
3. $9A^2$
4. $7A^2$

Q. In Kundt's tube experiment, a brass rod of length $1\text{m}$ is used and the average length of loop obtained in air is $10.3\text{cm}$ and in $C{O}_2$ is $8\text{cm}$. Calculate the speed of sound in brass and in $C{O}_2$.
Given, speed of sound in air is $350\text{m/s}$.

1. $5000\text{m/s},425.8\text{m/s}$
2. $3400\text{m/s},271.8\text{m/s}$
3. $2250\text{m/s},133.8\text{m/s}$
4. $4800\text{m/s},350.8\text{m/s}$

Q. A wavelength 0.60 cm is produced in air and it travels at a speed of 300 $m{s}^{-1}$. It will be an –

1. Audible wave
2. Infrasonic wave
3. Ultrasonic wave
4. None of the above

Q.

Ultrasonic waves of frequency 4.5 MHz are used to detect tumor in soft tissues. The speed of sound in tissue is 1.5 km s${}^{-1}$ and that in air is 340 m s${}^{-1}$. Find the wavelength of this ultrasonic wave in tissue.

1. 333 m

2. 1000 m

3. 10-4 m

4. 3.33 10 m

Q.

A source of sound of frequency $50Hz$ is producing longitudinal waves in air. The amplitude of vibrations of air particles is 5mm and the speed of the wave is $330m{s}^{-1}$. Write the equation of the wave.

1. $y=0.05sin[110\pi t-\frac{2\pi x}{3}]$
2. $y=5\times {10}^{-3}sin[100\pi t-\frac{10\pi x}{33}]$
3. $y=0.05sin[220\pi t-\frac{\pi x}{3}]$
4. $y=0.05sin[110\pi t-\frac{\pi x}{3}]$

Q. Consider a pulse created on the horizontal string highlighted. The net force applied by particles $A$ and $C$ on $B$ will be in

1. upward direction
2. downward direction
3. left direction
4. right direction

Q. What are the differences between infrasonic, audible and ultrasonic sound waves?

Q. What is 'diffraction of light'? Explain its two types.

Q. Two sinusoidal waves are defined by the expressions, $y_1=\left(2.00\right)\sin (20x-32t)$ and $y_2=\left(2.00\right)\sin (25x-40t)$ where $y_1,y_2$ and $x$ are in centimeters and $t$ is in seconds. What is the positive value of $x$, closest to the origin, for which the phase difference between the two waves is $\pi$ rad. at $t=2\text{s}$?

1. $0.06\text{cm}$
2. $0.10\text{cm}$
3. $0.12\text{cm}$
4. $0.15\text{cm}$

Q. Which one of the following rays cannot travel in vacuum?

1. Gamma rays
2. X rays
3. UV rays
4. Infrasonic rays

Q. A travelling wave pulse is given by $y=\frac{10}{5+{(x+2t)}^2}$. The amplitude and velocity of the pulse propagating are

1. $2units,-2units$
2. $2units,2units$
3. $10units,5units$
4. $10units,10units$

Q.

A body is vibrating 6000 times in a minute. If the velocity of sound is 360 m/s. Find

(i) the frequency in (Hz) (ii) Wavelength of sound

1. 100 Hz, 3.6 m

2. 600 Hz, 3.6 m

3. 60 Hz, 6 m

4. 6000 Hz, 0.06 m

Q. Which of the following is not true for the progressive wave $y=4sin2\pi (\frac{t}{0.02}-\frac{x}{100})$ where x and y are in cm and t in seconds

1. The wavelength is 100 cm
2. The frequency is 50 Hz
3. The velocity of propagation is 2 cm/s
4. The amplitude is 4 cm

Q. For the given two identical wave pulses, the resultant wave pulse when they interfere at a point at the same line of motion is -

1. 
2. 
3. 
4. 
   

Q. An open pipe is suddenly closed at one end. As a result the frequency of third harmonic of the closed pipe is found to be higher by 100 Hz. The fundamental frequency of open pipe is

1. 240 Hz
2. 480 Hz
3. 200 Hz
4. 30 Hz

Q.

A wave is described by the equation

$y=1.0mm\mathrm{sin\pi }\left(\frac{x}{2.0cm}-\frac{t}{0.01s}\right)$

(a) Find the time period and the wavelength?

(b) Write the equation for the velocity of the particles. Find the speed of the particle at $x=1.0cm$ at time $t=0.01s$

(c) What are the speeds of the particles at $x=3.0cm$, $5.0cm$ and $7.0cm$ at $t=0.01s$?

Q. The sound from a very high burst of fireworks takes 5 s to arrive at the observer. The burst occurs 1662 m above the observer and travels vertically through two stratifier layers of air, the top one of thickness
$d_1$ at $0^{\circ }C$ and the bottom one of thickness $d_2$ at ${20}^{\circ }C$. Then (assume velocity of sound at $0^{\circ }C$ is 330 m/s)

1. 
2. 
3. 
4. 

Q. Two identical wave pulses are formed as shown in the figure. If the first pulse undergoes a reflection from the wall, then the net amplitude of the interference between the second pulse and the first reflected pulse is -

1. $0\text{cm}$
2. $2\text{cm}$
3. $1.5\text{cm}$
4. $1\text{cm}$

Q.

Ultrasonic waves of frequency 4.5 MHz are used to detect tumor in soft tissues. The speed of sound in tissue is 1.5 km s${}^{-1}$ and that in air is 340 m s${}^{-1}$. Find the wavelength of this ultrasonic wave in tissue.

1. 333 m

2. 3.33 $\times$ 10${}^{-4}$ m

3. 1000 m

4. 10-4 m

Q. In a resonance tube the first resonance with a tuning fork occurs at $16$ cm and second at $49$ cm. If the velocity of sound is $330$ m/s, the frequency of tuning fork is :

1. $500$
2. $300$
3. $330$
4. $165$

Q. The slits in a Young's double slit experiment have equal widths and the source is placed symmetrically relative to the slits. The intensity at the central fringes is $I_0$. If one of the slits is closed, the intensity at this point will now be :-

Q. When a source of sound approaches a stationary observer with velocity $v_s$, then the apparent frequency observed by the observer will be $(v$ = velocity of sound$)$ :

1. $\frac{v_s}{v-v_s}n$
2. $\frac{v-v_s}{v}n$
3. $\frac{v+v_s}{v}n$
4. $\frac{v}{v-v_s}n$

Q. For a closed organ pipe three successive resonance frequencies are observed at $425Hz,595Hz$ and $765Hz$ respectively. If the speed of sound in air is $340m/s,$ then the length of the pipe is :

1. $2.0m$
2. $1.0m$
3. $0.4m$
4. $0.2m$

Q.

A horizontal rod is hit at one end. What kind of wave propagates in the rod if

(i) the hit is made vertically

(ii) the hit is made horizontally?

1. Transverse in both cases

2. Longitudinal in both cases

3. Longitudinal, transverse

4. Transverse, longitudinal

Q. From the following graph of photo current against collector plate potential, for two different intensities of light $I_1$ and $I_2$, one can conclude

1. $I_1=I_2$
2. $I_1>I_2$
3. $I_1<I_2$
4. Comparison is not possible