All questions of Wave Optics for NEET Exam

Effect of Immersing Young's Apparatus in Water on Fringe Width

When the Young's apparatus is immersed in water, the effect on the fringe width can be explained as follows:

1. Refractive Index of Water: Water has a higher refractive index than air. This means that light passing through water will be bent more than in air.

2. Path Difference: Path difference is the difference in the distance traveled by two waves from the source to the point where they interfere with each other. When the apparatus is immersed in water, the path difference between the two waves will change due to the change in refractive index.

3. Decrease in Fringe Width: As the path difference changes, the interference pattern will also change. The fringe width will decrease because the change in the path difference will cause the interference pattern to become more spread out.

4. Explanation: The fringe width is inversely proportional to the square root of the refractive index. Since the refractive index of water is higher than air, the fringe width will decrease when the apparatus is immersed in water.

Conclusion

In conclusion, when the Young's apparatus is immersed in water, the fringe width will decrease due to the change in refractive index, which leads to a change in the path difference and the interference pattern.

Transverse and longitudinal waves. Light and other types of electromagnetic radiation are transverse waves. Water waves and S waves (a type of seismic wave) are also transverse waves. In transverse waves, the vibrations are at right angles to the direction of travel.

If one illuminates two parallel slits, the light from the two slits again interferes. Here the interference is a more pronounced pattern with a series of alternating light and dark bands. ... He also proposed (as a thought experiment) that if detectors were placed before each slit, the interference pattern would disappear.

Two wave sources are perfectly coherent if their frequency and waveform are identical and their phase difference is constant. So, option c is correct.

Answer A is right , because c. = frequency×wavelength
that means red light will have larger speed since it has larger wavelength
also c is inversely proportional to refractive index
Hence red light will be slower in this given glass than violet

Rays are always perpendicular to the wave fronts.... wave fronts move right angles to it self...

Option A ....Since the light coming from the distance star to the earth will be at Infinity , the rays coming from it will be parallel rays , thus the wavefront will be a plane .

Fringe width is inversly prop to dist betweenslit so it is double

From malu's law, If I0 is intensity of plane polarised light incident on an analyser and (thete) is the angle between axes of polariser and analyser, then intensity of polarised light transmitted from analyser ,I = I0 cos(^2) thete, ie, when (thete)=0, cos(^2) 0=1, then I= I0 ie, the transmission axes of polariser and analyser are paralell.

That is the definition of diffraction. The bending of light around obstacles with a size comparable to its own wavelength.

C

Therefore if monochromatic light in Young's interference experiment is replaced by white light, then the waves of each wavelength form their separate interference patterns. The resultant effect of all these patterns is obtained on the screen. i.e., the waves of all colours reach at mid point M in same phase we will see​.a few coloured bands and then uniform illumination

Phase difference between two coherent sources should be zero.

Coherent Sources:
Coherent sources are the sources of light that emit light waves of the same frequency and have a constant phase difference with respect to each other. When two coherent sources emit light waves, the waves superimpose to form an interference pattern.

Phase Difference:
The phase difference is the difference in the phase of two waves at a given point in space and time. It is measured in radians or degrees. When two coherent sources emit light waves, the phase difference between them determines the interference pattern.

Explanation:
When two coherent sources emit light waves of the same frequency and zero phase difference, the waves superimpose constructively and form a bright fringe in the interference pattern. If the phase difference between the two sources is not zero, the waves may superimpose destructively, resulting in a dark fringe.

Therefore, to obtain a clear interference pattern, the phase difference between the two sources should be zero. This can be achieved by ensuring that the two sources are of the same frequency and are in phase with each other.

Conclusion:
In conclusion, the phase difference between two coherent sources should be zero to obtain a clear interference pattern. This can be achieved by ensuring that the two sources are of the same frequency and are in phase with each other.

This is in accordance with Brewsters law. When light is incident. When light is incident at Brewsters angle then the refracted and reflected ray are perpendicular to reach other.

Diffraction is defined as the bending of light around the corners of the obstacle or aperture into the region Of geometrical shadow if the obstacle. Diffraction occurs with all waves, including sound waves, water waves and electromagnetic waves.

If a medium has the same refractive index at every point in all directions, then the waveform obtained from a point source in such a medium is spherical since the wave travels in all directions at the same speed. Such a medium is known as isotropic medium. So, the assertion and reason both are true and the reason explain the assertion properly.

Assertion: In YDSE, if a thin film is introduced in front of the upper slit, then the fringe pattern shifts in the downward direction.

Reason: In YDSE if the slit widths are unequal, the minima will be completely dark.

The correct answer is option 'D' - both the Assertion and Reason are incorrect.

Explanation:

Assertion: In YDSE, if a thin film is introduced in front of the upper slit, then the fringe pattern shifts in the downward direction.

This assertion is incorrect. When a thin film is introduced in front of the upper slit, it does not cause a shift in the fringe pattern in the downward direction. Instead, it leads to the formation of interference fringes in the form of concentric circles around the central bright fringe. This phenomenon is known as Newton's rings.

Reason: In YDSE if the slit widths are unequal, the minima will be completely dark.

This reason is also incorrect. In a Young's double-slit experiment, when the slit widths are unequal, it does not necessarily result in completely dark minima. The intensity of the minima may vary depending on the relative widths of the slits, but they will not be completely dark. The interference pattern formed by the superposition of the waves from the two slits will still exhibit alternating bright and dark fringes.

Therefore, both the Assertion and Reason are incorrect, leading to the correct answer being option 'D'.

Understanding Interference Patterns
Interference patterns arise when two coherent light sources combine their wavefronts. The characteristics of these patterns depend on several factors, including the distance between the sources.
Assertion Explained
- The assertion states that no interference pattern is detected when the two coherent sources are infinitely close to each other.
- This is true because the overlapping waves from two sources that are extremely close become indistinguishable; thus, they cannot create a distinct interference pattern.
Reason Explained
- The reason asserts that the fringe width is inversely proportional to the distance between the two sources.
- This statement is also correct. When the distance between the sources decreases, the fringe width (the distance between bright or dark fringes) increases, leading to a less discernible pattern.
Relationship Between Assertion and Reason
- Both the assertion and reason are accurate.
- The reason helps clarify why the assertion is true: as the sources get closer, the fringe width increases, making the interference pattern less noticeable.
Conclusion
- Therefore, the correct response is option 'A': both Assertion and Reason are correct, and the Reason is a valid explanation for the Assertion.
This understanding of interference patterns is crucial in the study of wave optics and illustrates the relationship between distance and visibility of interference effects.

Assertion: In Young’s double slit experiment, if the wavelength of incident monochromatic light is doubled, the number of bright fringes on the screen will increase.
Reason: The maximum number of bright fringes on the screen is inversely proportional to the wavelength of light used.

To understand why the correct answer is option 'A', let's break down the Assertion and Reason separately and then see how they relate to each other.

Assertion: In Young’s double slit experiment, if the wavelength of incident monochromatic light is doubled, the number of bright fringes on the screen will increase.

In Young's double-slit experiment, a beam of monochromatic light is passed through two slits, creating an interference pattern on a screen placed behind the slits. The interference pattern consists of alternating bright and dark fringes.

When the wavelength of the incident light is doubled, it means that the light waves are becoming longer. The distance between the bright fringes in the interference pattern is determined by the wavelength of light. A longer wavelength means a larger distance between the fringes.

So, if the wavelength is doubled, the distance between the bright fringes will also double. As a result, the number of bright fringes that can fit on the screen will increase. Therefore, the assertion is correct.

Reason: The maximum number of bright fringes on the screen is inversely proportional to the wavelength of light used.

The reason states that the maximum number of bright fringes on the screen is inversely proportional to the wavelength of light used. In other words, as the wavelength increases, the number of bright fringes decreases.

This reason is correct because the distance between the bright fringes is directly related to the wavelength of light. The formula for calculating the distance between the fringes is given by:

Distance between fringes = (wavelength * distance between slits) / (distance to the screen)

As the wavelength increases, the distance between fringes increases, and therefore, the number of fringes that can fit on the screen decreases. This is because the screen has a limited size, and as the distance between fringes increases, fewer fringes can fit within that limited space.

Therefore, the reason is a correct explanation of the assertion.

Conclusion:

Both the assertion and the reason are correct, and the reason is a correct explanation of the assertion. Hence, the correct answer is option 'A'.

Assertion (A): Diffraction takes place with all types of waves.
Reason (R): Diffraction is perceptible when the wavelength of the wave is comparable to the dimension of the diffracting device.

Explanation:
Diffration and its occurrence:
- Diffraction is the bending or spreading of waves as they pass through an opening or around obstacles.
- It occurs with all types of waves, including light waves, sound waves, water waves, and even matter waves such as electrons.
- When a wave encounters an obstacle or passes through an opening, it bends and spreads out, resulting in diffraction.

Wavelength and Diffraction:
- The wavelength of a wave is the distance between two consecutive points in a wave that are in phase.
- Diffraction is perceptible when the wavelength of the wave is comparable to the dimension of the diffracting device.
- In other words, when the size of the opening or obstacle is similar to the wavelength of the wave, significant diffraction occurs.
- The diffraction pattern depends on the ratio of the wavelength of the wave to the size of the opening or obstacle.

Explanation of Assertion and Reason:
- Assertion (A) states that diffraction takes place with all types of waves, which is true.
- Reason (R) states that diffraction is perceptible when the wavelength of the wave is comparable to the dimension of the diffracting device, which is also true.
- The reason provided in (R) correctly explains why diffraction occurs.

Conclusion:
- Both Assertion (A) and Reason (R) are true.
- Reason (R) is the correct explanation of Assertion (A).
- Therefore, the correct answer is option 'B'.

Understanding the nature of light:
Light has been a subject of scientific investigation for centuries, and its nature has been a topic of debate among scientists. Initially, scientists believed that light behaves solely like a particle, known as the corpuscular theory of light. However, with the advent of experiments and further research, it became evident that light exhibits characteristics of both particles and waves. This understanding led to the development of the wave-particle duality theory, which states that light can behave as both a particle and a wave, depending on the experimental conditions and the phenomenon under study.

Particle-like behavior of light:
When light interacts with matter, it exhibits certain particle-like characteristics. These characteristics include the ability to transfer energy and momentum in discrete amounts called photons. Photons have no mass but possess energy proportional to their frequency, according to the equation E=hf (where E is energy, h is Planck's constant, and f is the frequency of light). This particle-like behavior is observed in phenomena like the photoelectric effect, where light incident on a metal surface causes the emission of electrons.

Wave-like behavior of light:
On the other hand, light also exhibits wave-like characteristics. When light propagates through space, it shows properties such as diffraction, interference, and polarization. Diffraction refers to the bending of light around obstacles or through narrow openings, similar to how waves bend around objects in water. Interference occurs when two or more light waves superpose, either constructively (resulting in bright regions) or destructively (resulting in dark regions), depending on their relative phase. Polarization refers to the alignment of the electric field vectors of light waves, which can be manipulated using filters.

Complementary nature of particle and wave descriptions:
The wave-particle duality theory suggests that light is neither exclusively a particle nor a wave, but a combination of both. The particle and wave approaches are complementary and help us understand different phenomena associated with light. For instance, the particle nature of light explains phenomena like the photoelectric effect and the emission and absorption of photons, while the wave nature of light explains phenomena like interference and diffraction.

Conclusion:
In conclusion, light is best described as exhibiting both particle-like and wave-like behavior. The particle and wave approaches are essential in understanding different aspects of light and its interaction with matter. While the particle behavior explains discrete energy transfer and certain phenomena, the wave behavior explains properties such as diffraction, interference, and polarization. Therefore, option 'A' is the correct answer as it acknowledges the complementary nature of the particle and wave descriptions of light.