A convex lens of diameter 8.0cm is used to focus a parallel beam of light of wavelength 620nm. If the light be focused at a distance of 20cm from the lens, what would be the radius of the central bright spot formed?
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Light Waves questions
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Light of wavelength 560nm goes through a pinhole of diameter 0.20mm and falls on a wall at a distance of 2.00m. What will be the radius of the central bright spot formed on the wall?
A plate of thickness t made of a material of refractive index $\mu$ is placed in front of one of the slits in a double slit experiment.
View full solution →- Find the change in the optical path due to introduction of the plate.
- What should be the minimum thickness t which will make the intensity at the centre of the fringe pattern zero? Wavelength of the light used is $\lambda$. Neglect any absorption of light in the plate.
A parallel beam of monochromatic light is used in a Young's double slit experiment. The slits are separated by a distance d and the screen is placed parallel to the plane of the slits. Show that if the incident beam makes an angle $\theta=\sin^{-1}\Big(\frac{\lambda}{2\text{D}}\Big)$ with the normal to the plane of the slits, there will be a dark fringe at the centre P0 of the pattern.
View full solution →The speed of the yellow light in a certain liquid is 2.4 × 108m/s. Find the refractive index of the liquid.
A narrow slit S transmitting light of wavelength $\lambda$ is placed a distance d above a large plane mirror as shown in figure (17-E1). The light coming directly from the slit and that coming after the reflection interfere at a screen $\sum$ placed at a distance D from the slit.
View full solution →- What will be the intensity at a point just above the mirror, i.e., just above O?
- At what distance from 0 does the first maximum occur?
The index of refraction of fused quartz is 1.472 for light of wavelength 400nm and is 1.452 for light of wavelength 760nm. Find the speeds of light of these wavelengths in fused quartz.
Find the range of frequency of light that is visible to an average human being $(400\text{nm}<\lambda<700\text{nm}).$
View full solution →Can we perform Young's double slit experiment with sound waves? To get a reasonable "fringe pattern", what should be the order of separation between the slits? How can the bright fringes and the dark fringes be detected in this case?
If the separation between the slits in a Young's double slit experiment is increased, what happens to the fringe-width? If the separation is increased too much, will the fringe pattern remain detectable?
Plane microwaves are incident on a long slit having a width of 5.0cm. Calculate the wavelength of the microwaves if the first diffraction minimum is formed at $\theta=30^\circ.$
View full solution →Find the thickness of a plate which will produce a change in optical path equal to half the wavelength $\lambda$ of the light passing through it normally. The refractive index of the plate is $\mu$.
View full solution →Consider the situation of the previous problem. If the mirror reflects only 64% of the light energy falling on it, what will be the ratio of the maximum to the minimum intensity in the interference pattern observed on the screen?
TV signals broadcast by Delhi studio cannot be directly received at Patna which is about 1000km away. But the same signal goes some 36000km away to a satellite, gets reflected and is then received at Patna. Explain.
Why don't we have interference when two candles are placed close to each other and the intensity is seen at a distant screen? What happens if the candles are replaced by laser sources?
The inverse square law of intensity $\Big(\text{i.e., the intensity}\propto\frac{1}{\text{r}^2}\Big)$ is valid for a:
View full solution →- Point source.
- Line source.
- Plane source.
- Cylindrical source.
The slits in a Young's double slit experiment have equal width and the source is placed symmetrically with respect to the slits. The intensity at the central fringe is I0. If one of the slits is closed, the intensity at this point will be:
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$\text{I}_0$
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$\frac{\text{I}_0}{4}$
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$\frac{\text{I}_0}{2}$
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$4\text{I}_0$
Suppose the medium in the previous question is water. Select the correct option(s) from the list given in that question.
View full solution →- vA > vB > vC
- vA < vB < vC
- vA = vB = vC
- $\text{v}_\text{B}=\frac{1}{2}(\text{v}_\text{A}+\text{v}_\text{C})$
The wavefronts of a light wave travelling in vacuum are given by x + y + z = c. The angle made by the direction of propagation of light with the X-axis is:
View full solution →-
$0^\circ$
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$45^\circ$
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$90^\circ$
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$\cos^{-1}\Big(\frac{1}{\sqrt{3}}\Big)$
Three observers A, B and C measure the speed of light coming from a source to be vA, 0B and vc. The observer A moves towards the source and C moves away from the source at the same speed. The observer B stays stationary. The surrounding space is vacuum everywhere.
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$\text{v}_\text{A}>\text{v}_\text{B}>\text{v}_\text{C}.$
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$\text{v}_\text{A}<\text{v}_\text{B}<\text{v}_\text{C}$
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$\text{v}_\text{A}=\text{v}_\text{B}=\text{v}_\text{C}$
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$\text{v}_\text{B}=\frac{1}{2}(\text{v}_\text{A}+\text{v}_\text{C})$
A parallel beam of white light is incident normally on a water film 1.0 × 10-4cm thick. Find the wavelength in the visible range (400nm - 700nm) which are strongly transmitted by the film. Refractive index of water = 1.33.
A mica strip and a polysterene strip are fitted on the two slits of a double slit apparatus. The thickness of the strips is 0.50mm and the separation between the slits is 0.12cm. The refractive index of mica and polysterene are 1.58 and 1.55 respectively for the light of wavelength 590nm which is used in the experiment. The interference is observed on a screen a distance one meter away.
- What would be the fringe-width?
- At what distance from the centre will the first maximum be located?
In a Young's double slit interference experiment the fringe pattern is observed on a screen placed at a distance D from the slits. The slits are separated by a distance d and are illuminated by monochromatic light of wavelength $\lambda$. Find the distance from the central point where the intensity falls to,
View full solution →- Half the maximum.
- One fourth of the maximum.
A thin paper of thickness 0.02mm having a refractive index 1.45 is pasted across one of the slits in a Young's double slit experiment. The paper transmits $\frac{4}{9}$ of the light energy falling on it.
View full solution →- Find the ratio of the maximum intensity to the minimum intensity in the fringe pattern.
- How many fringes will cross through the centre if an identical paper piece is pasted on the other slit also? The wavelength of the light used is 600nm.
Figure shows three equidistant slits being illuminated by a monochromatic parallel beam of light. Let $\text{BP}_0-\text{AP}=\frac{\lambda}{3}$ and $\text{D}>\lambda.$
View full solution →- Show that in this case $\text{d}=\sqrt{\frac{2\lambda\text{D}}{3}}.$
- Show that the intensity at P, is three times the intensity due to any of the three slits individually.
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