Doppler Effect in Light Waves

Q. A speeding motorcyclist sees traffic jam ahead of him. He slows down to 36 km/hour. He finds that traffic has eased and a car moving ahead of him at 18 km/hour is honking at a frequency of 1392 Hz. If the speed of sound is 343 m/s, the frequency of the honk as heard by him will be

1. 1332 Hz
2. 1372 Hz
3. 1454 Hz
4. 1412 Hz

Q. Plz send some topics on physics investigatory project class 11

Q. The potential difference that must be applied to stop the fastest photo electrons emitted by a nickel surface, having work function $5.01\text{eV}$, when ultraviolet light of $200\text{nm}$ falls on it, must be

1. $\text{-1.2 V}$
2. $\text{-2.4 V}$
3. $\text{1.2 V}$
4. $\text{2.4 V}$

Q.

A sound source $S$ is moving along a straight track with speed $v$, and is emitting, the sound of frequency $v_o$ (see figure). An observer is standing at a finite distance, at the point $O$, from the track. The time variation of frequency heard by the observer is best represented by ($t_o$ represents the instant when the distance between the source and observer is minimum).

1. 

2. 

3. 

4. 

Q.

A train, standing at the outer signal of a railway station blows a whistle of frequency 400 Hz in still air. (i) What is the frequency of the whistle for a platform observer when the train (a) approaches the platform with a speed of $10m{s}^{-1}$ , (b) recedes from the platform with a speed of $10m{s}^{-1}$ ? (ii) What is the speed of sound in each case? The speed of sound in still air can be taken as $340m{s}^{-1}$

Q. An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency $10\text{GHz}$. What is the frequency in GHz of the microwave measured by the observer?
(speed of light $=3\times {10}^8{\text{ms}}^{-1}$). Answer the nearest integer.

Q.

A SONAR system fixed in a submarine operates at a frequency 40.0 kHz. An enemy submarine moves towards the SONAR with a speed of 360 km/hr. What is the frequency of sound reflected by the submarine? Take the speed of sound in water to be 1450 m/s.

Q.

A stationary source emits sound of frequency $f_0=492Hz$. The sound is reflected by a large car approaching the source with a speed of $2m{s}^{-1}$. The reflected signal is received by the source and superposed with the original. The beat frequency of the resulting signal is $Hz$. (Given that the speed of sound in air is $330m{s}^{-1}$ and the car reflects the sound at the frequency it has received).

Q. A wall is moving with velocity u and a source of sound moves with velocity u/2 in the same direction as shown in the figure. Assuming that the sound travels with velocity 10u, the ratio of incident sound wavelength on the wall to the reflected sound wavelength by the wall is equal to

1. 5:4
2. 9:11
3. 11:9
4. 4:5

Q.

A very thin transparent film of soap solution of negligible thickness is seen under reflection of white light. Then the colour of the film appear to be :

A) blue

B) black

C) red

D) yellow

Q. Two coherent sources separated by distance $d$ are radiating in phase having wavelength $\lambda$. A detector moves in a big circle around the two sources in the plane of the two sources. The angular position of $n=4$ interference maxima is given as

1. ${\cos }^{-1}\left(\frac{\lambda }{4d}\right)$
2. ${\tan }^{-1}\left(\frac{\lambda }{4d}\right)$
3. ${\sin }^{-1}\left(\frac{4\lambda }{d}\right)$
4. ${\cos }^{-1}\left(\frac{4\lambda }{d}\right)$

Q. Light takes t1 sec to travel a distance x cm.and Same light take t2 sec to travel 10x cm in medium . The critical angle of corresponding medium is .

Q.

What is a wavelet in physics?

Q.

A train, standing in a station-yard, blows a whistle of frequency 400 Hz in still air. The wind starts blowing in the direction from the yard to the station with at a speed of $10m{s}^{-1}$. What are the frequency, wavelength, and speed of sound for an observer standing on the station’s platform? Is the situation exactly identical to the case when the air is still and the observer runs towards the yard at a speed of $10m{s}^{-1}$ ? The speed of sound in still air can be taken as $340m{s}^{-1}$

Q. The following graph shows how the inverse of magnification $\frac{1}{m}$ produced by a thin convex lens varies with distance u. What is the focal length of lens used?

1. $\frac{b}{c}$
2. $\frac{b}{ca}$
3. $\frac{bc}{a}$
4. $\frac{c}{b}$

Q. White light is passed through a double slit and interference is observed on a screen $1.5\text{m}$ away. The separation between the slits is $0.3\text{mm}$. The first violet and red fringes are formed $2.0\text{mm}$ and $3.5\text{mm}$ away from the central white fringe. The difference in wavelengths of red and violet light is nm

Q.

An isotropic point source having radiation power P is located on the axis of an ideal mirror plate. The distance between the source and the plate centre is n times the radius of the plate. In terms of photon theory find the force that light exerts on the plate.(c denotes speed of light) ?

1. $\frac{P}{2C}\left[\frac{1}{1+n^2}\right]$
2. $\frac{P}{2C}\left[\frac{1}{1+2n^2}\right]$
3. $\frac{P}{C}\left[\frac{1}{1+n^2}\right]$
4. $\frac{P}{C}\left[\frac{1}{1+2n}\right]$

Q. A horizontal stretched string fixed at both ends, is vibrating in its fifth harmonic according to the equation, $y(x,t)=\left(0.01\text{m}\right)\sin \left[\right(62.8{\text{m}}^{-1}\left)x\right]\cos \left[\right(628{\text{s}}^{-1}\left)t\right]$. Assume $\pi =3.14$, which of the following is/are the correct statements.

1. The number of nodes is $5$
2. The length of the string is $0.25\text{m}$
3. The maximum displacement of the mid-point of the string from its equilibrium position is $0.01\text{m}$
4. The fundamental frequency is $50\text{Hz}$

Q. The frequency of the whistle of an engine appears to be ${\left(\frac{5}{6}\right)}^{th}$ of the original frequency , when it passes a stationary observer. If the speed of sound in air is $350\text{m/s}$, then the speed of the engine is:

[Assume, medium is stationary and the original frequency of the whistle is measured when the source and observer are at rest]

1. $35\text{m/s}$
2. $70\text{m/s}$
3. $105\text{m/s}$
4. $140\text{m/s}$

Q.

Is an LED a coherent light source ?

Q.

If the angles $A$, $B$ and $C$ of a triangle are in an arithmetic progression and if $a$, $b$ and $c$ denote the lengths of the sides opposite to $A$, $B$ and $C$ respectively, then the value of the expression $\left(\frac{a}{c}\right)\sin 2C+\left(\frac{c}{a}\right)\sin 2A$ is

1. $\frac{1}{2}$

2. $\frac{\sqrt{3}}{2}$

3. $1$

4. $\sqrt{3}$

Q. Two coherent sources of light $S_1\text{and}{S}_2$, equidistant from the origin, are separated by a distance $2\lambda$ as shown. They emit light of wavelength $\lambda$. Interference is observed on a screen placed along a large circle of radius $R$. A point on the circumference is found to be a point of constructive interference. Then angle $\theta$ (in the first quadrant of the circle) is,
(Consider that the vertical diameter is the point where central bright fringe lies)

1. ${45}^{\circ }$
2. ${30}^{\circ }$
3. ${60}^{\circ }$
4. $\text{Not possible in the first quadrant}$

Q. dispersive power of prism why not depend upon size and angle of prism as the formula of dispersive power derive we use min.deviation=(μ-1)A is only applicable for small angle of pris

Q.

Are all transverse waves polarized?

Q. In a $YDSE$, both slits produce equal intensities on the screen. A $100\%$ transparent thin film is placed in front of one of the slits. Now, the intensity on the centre becomes $75\%$ of the previous intensity. The wavelength of light is $6000\dot{\text{A}}$ and refractive index of glass is $1.5$. The minimum thickness of the glass slab is

1. $0.2\mu \text{m}$
2. $0.3\mu \text{m}$
3. $0.4\mu \text{m}$
4. $0.5\mu \text{m}$

Q.

Two submarines are approaching each other in a calm sea. The first submarine travels at a speed of 36 km $h^{-1}$ and the other at 54 km $h^{-1}$' relative to the water. The first submarine sends a sound signal (sound waves in water are also called sonar) at a frequency of 2000 Hz. (a) At what frequency is this signal received by the second submarine ? (b) The signal is reflected from the second submarine. At what frequency is this signal received by the first submarine. Take the speed of the sound wave in water to be $1500m{s}^{-1}$

Q. The light from the sun is found to have a maximum intensity near the wavelength of $470\text{nm}$. Assuming that the surface of the sun emits as a blackbody, calculate the temperature of the surface of the sun. Given: $b\left(\text{Wein's constant}\right)=0.288\text{cm}K$

1. $5110K$
2. $4588K$
3. $6130K$
4. $7123K$

Q.

A point object is placed on the principal. axis of a convex lens (f= 15 cm) at a distance of 30 cm from it. A glass plate $(\mu =1.50)$ of thickness 1 cm is placed on the other side of the lens perpendicular to the axis. Locate the image of the point object.

Q.

Two factories are sounding their sirens at $800Hz$. A man goes from one factory to another at a speed of $2m/s$. The velocity of sound is $320m/s$. The number of beats heard by the person in one second will be.

Q. For sound waves, the Doppler formula for frequency shift differsslightly between the two situations: (i) source at rest; observermoving, and (ii) source moving; observer at rest. The exact Dopplerformulas for the case of light waves in vacuum are, however, strictlyidentical for these situations. Explain why this should be so. Wouldyou expect the formulas to be strictly identical for the two situationsin case of light travelling in a medium?