Advertisements
Advertisements
प्रश्न
A parallel beam of light of wavelength 560 nm falls on a thin film of oil (refractive index = 1.4). What should be the minimum thickness of the film so that it strongly reflects the light?
Advertisements
उत्तर
Given:-
Wavelength of light used,
\[\lambda = 560 \times {10}^{- 9} m\]
Refractive index of the oil film, \[\mu = 1 . 4\]
Let the thickness of the film for strong reflection be t.
The condition for strong reflection is
\[2\mu t = \left( 2n + 1 \right)\frac{\lambda}{2}\]
\[ \Rightarrow t = \left( 2n + 1 \right)\frac{\lambda}{4\mu}\]
where n is an integer.
For minimum thickness, putting n = 0, we get
\[t = \frac{\lambda}{4\mu}\]
\[ = \frac{560 \times {10}^{- 9}}{4 \times 1 . 4}\]
\[ = {10}^{- 7} m = 100 nm\]
Therefore, the minimum thickness of the oil film so that it strongly reflects the light is 100 nm.
APPEARS IN
संबंधित प्रश्न
Monochromatic light of wavelength 589 nm is incident from air on a water surface. What are the wavelength, frequency and speed of (a) reflected and (b) refracted light? Refractive index of water is 1.33.
Define a wavefront.
If we put a cardboard (say 20 cm × 20 cm) between a light source and our eyes, we can't see the light. But when we put the same cardboard between a sound source and out ear, we hear the sound almost clearly. Explain.
Light is _______________ .
The inverse square law of intensity \[\left(\text{i.e. the intensity }\infty \frac{1}{r^2}\right)\] is valid for a ____________ .
Three observers A, B and C measure the speed of light coming from a source to be νA, νBand νC. A moves towards the source and C moves away from the source at the same speed. B remains stationary. The surrounding space is vacuum everywhere.
(a) \[\nu_A > \nu_B > \nu_C\]
(b) \[\nu_A < \nu_B < \nu_C\]
(c) \[\nu_A = \nu_B = \nu_C\]
(d) \[\nu_B = \frac{1}{2}\left( \nu_A + \nu_C \right)\]
Three observers A, B and C measure the speed of light coming from a source to be νA, νBand νC. A moves towards the source and C moves away from the source at the same speed. B remains stationary. The surrounding space is water everywhere.
(a) \[\nu_A > \nu_B > \nu_C\]
(b) \[\nu_A < \nu_B < \nu_C\]
(c) \[\nu_A = \nu_B = \nu_C\]
(d) \[\nu_B = \frac{1}{2}\left( \nu_A + \nu_C \right)\]
Find the range of frequency of light that is visible to an average human being
\[\left( 400\text{ nm }< \lambda < 700\text{ nm}\right)\]
Find the thickness of a plate which will produce a change in optical path equal to half the wavelength λ of the light passing through it normally. The refractive index of the plate is μ.
A parallel beam of white light is incident normally on a water film 1.0 × 10−4 cm thick. Find the wavelengths in the visible range (400 nm − 700 nm) which are strongly transmitted by the film. Refractive index of water = 1.33.
The optical path of a ray of light of a given wavelength travelling a distance of 3 cm in flint glass having refractive index 1.6 is the same as that on travelling a distance x cm through a medium having a refractive index 1.25. Determine the value of x.
Answer in brief:
The distance between two consecutive bright fringes in a biprism experiment using the light of wavelength 6000 Å is 0.32 mm by how much will the distance change if light of wavelength 4800 Å is used?
A parallel beam of green light of wavelength 550 nm passes through a slit of width 0.4 mm. The intensity pattern of the transmitted light is seen on a screen that is 40 cm away. What is the distance between the two first-order minima?
Monochromatic electromagnetic radiation from a distant source passes through a slit. The diffraction pattern is observed on a screen 2.50 m from the slit. If the width of the central maximum is 6.00 mm, what is the slit width if the wavelength is
(a) 500 nm (visible light)
(b) 50 µm (infrared radiation)
(c) 0.500 nm (X rays)?
A Plane Wavefront of light of wavelength 5500 A.U. is incident on two slits in a screen perpendicular to the direction of light rays. If the total separation of 10 bright fringes on a screen 2 m away is 2 cm. Find the distance between the slits.
Two vectors of the same magnitude have a resultant equal to either of the two vectors. The angle between two vectors is
Light behaves as _________.
Emission and absorption is best described by ______.
A ray is an imaginary line ______.
State the theories which were proposed to explain nature of light.
