A thin film of liquid is held in a horizontal circular ring, with air on both sides of the film. A beam of light at wavelength 550 nm is directed perpendicularly onto the film, and the intensity I of its reflection is monitored. Figure 35-47 gives intensity I as a function of time t ; the horizontal scale is set by t s = 20.0 s. The intensity changes because of evaporation from the two sides of the film. Assume that the film is flat and has parallel sides, a radius of 1.80 cm, and an index of refraction of 1.40. Also assume that the films volume decreases at a constant rate. Find that rate. Figure 35-47 Problem 78.
A thin film of liquid is held in a horizontal circular ring, with air on both sides of the film. A beam of light at wavelength 550 nm is directed perpendicularly onto the film, and the intensity I of its reflection is monitored. Figure 35-47 gives intensity I as a function of time t ; the horizontal scale is set by t s = 20.0 s. The intensity changes because of evaporation from the two sides of the film. Assume that the film is flat and has parallel sides, a radius of 1.80 cm, and an index of refraction of 1.40. Also assume that the films volume decreases at a constant rate. Find that rate. Figure 35-47 Problem 78.
A thin film of liquid is held in a horizontal circular ring, with air on both sides of the film. A beam of light at wavelength 550 nm is directed perpendicularly onto the film, and the intensity I of its reflection is monitored. Figure 35-47 gives intensity I as a function of time t; the horizontal scale is set by ts = 20.0 s. The intensity changes because of evaporation from the two sides of the film. Assume that the film is flat and has parallel sides, a radius of 1.80 cm, and an index of refraction of 1.40. Also assume that the films volume decreases at a constant rate. Find that rate.
www In Fig. 35-48,
an airtight chamber of length d
5.0 cm is placed in one of the arms
of a Michelson interferometer. (The
glass window on each end of the cham-
ber has negligible thickness.) Light of
wavelength A = 500 nm is used.
Evacuating the air from the chamber
causes a shift of 60 bright fringes. From
these data and to six significant figures,
81 SSM
Mirror
%3D
Source
Mirror
To vacuum
find the index of refraction of air at
pump
atmospheric pressure.
92 Figure 35-56a shows two light rays that are initially in phase
as they travel upward through a block of plastic, with wavelength
400 nm as measured in air. Light ray r, exits directly into air.
However, before light ray r, exits into air, it travels through a liquid
in a hollow cylinder within the plastic. Initially the height Lúq of the
liquid is 40.0 um, but then the liquid begins to evaporate. Let o be
the phase difference between rays r, and r, once they both exit into
the air. Figure 35-56b shows versus the liquid's height Lig
until the liquid disappears, with o given in terms of wavelength and
the horizontal scale set by L, = 40.00 µm. What are (a) the index of
refraction of the plastic and (b) the index of refraction of the
liquid?
60
L'ia
20
- Plastic
L,
Liq (um)
(a)
(6)
(Y) ¢
A thin layer of oil with index of refraction no = 1.47 is floating above the water. The index of refraction of water is nw = 1.3. The index of refraction of air is na = 1. A light with wavelength λ = 325 nm goes in from the air to oil and water.
Part (a) Express the wavelength of the light in the oil, λo, in terms of λ and no.
Part (b) Express the minimum thickness of the film that will result in destructive interference, tmin, in terms of λo. Part (c) Express tmin in terms of λ and no. Part (d) Solve for the numerical value of tmin in nm.
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