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Figure illustrates an interferometer used in measurement of refractive indices of transparent substances. Here S is a narrow slit illuminated by a monochromatic light with wavelength λ=589 nm, 1 and 2 are identical tubes with air of length l=10.0 cm each, D is a diaphragm with two slits. After the air in tube 1 was replaced with ammonia gas, the interference pattern on the screen Sc was displaced upward by N=17 fringes. The refractive index of air is equal to n=1.000277. Determine the refractive index of ammonia gas.

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Important Questions on OPTICS

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Problems in General Physics>Chapter 5 - OPTICS>THERMAL RADIATION>Q 5.247.
The temperature of one of the two heated black bodies is T1=2500 K. Find the temperature of the other body, if the wavelength corresponding to its maximum emissive capacity exceeds by Δλ=0.50 μm the wavelength corresponding to the maximum emissive capacity of the first black body. Wein's constant, b=2.898×10-3 mK
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Problems in General Physics>Chapter 5 - OPTICS>THERMAL RADIATION>Q 5.249.
The spectral composition of solar radiation is much the same as that of a black body whose maximum emission corresponds to the wavelength 0.48 μm. Find the mass lost by the Sun every second due to radiation. Evaluate the time interval during which the mass of the Sun diminishes by 1 per cent. Wein's constant b=2.9×10-3 mK, mass of Sun is 1.97×1030 kg, speed of light c=3×108 ms-1, the Stefan-Boltzmann constant σ=5.67×10-8 J s-1, emissivity for Sun e=1 and the radius of the Sun is 6.95×108 m.
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Problems in General Physics>Chapter 5 - OPTICS>THERMAL RADIATION>Q 5.251.
A copper ball of diameter d=1.2 cm was placed in an evacuated vessel whose walls are kept at the absolute zero temperature. The initial temperature of the ball is T0=300 K. Assuming the surface of the ball to be absolutely black, find how soon its temperature decreases η=2.0 times. Density of copper is 8.9 gcm-3, specific heat capacity of copper is 0.39 Jg-1K-1, the Stefan-Boltzmann constant σ=5.67×10-8 Js-1.
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Problems in General Physics>Chapter 5 - OPTICS>THERMAL RADIATION>Q 5.260.

An isotropic point source emits light with wavelength λ=589 nm. The radiation power of the source is P=10 W. Find

(a) the mean density of the flow of photons at a distance r=2.0 m from the source.

(b) the distance between the source and the point at which the mean concentration of photons is equal to n=100 cm-3.

Planck's constant h=6.626×10-34 JHz-1 and speed of light c=3×108 ms-1

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Problems in General Physics>Chapter 5 - OPTICS>THERMAL RADIATION>Q 5.261.
From the standpoint of the corpuscular theory, demonstrate that the momentum transferred by a beam of parallel light rays per unit time does not depend on its spectral composition but depends only on the energy flux Φe.
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Problems in General Physics>Chapter 5 - OPTICS>THERMAL RADIATION>Q 5.262.
A laser emits a light pulse of duration τ=0.13 ms and energy E=10 J. Find the mean pressure exerted by such a light pulse when it is focused into a spot of diameter d=10 μm on a surface perpendicular to the beam and possessing a reflection coefficient ρ=0.50, speed of light c=3×108 ms-1.
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Problems in General Physics>Chapter 5 - OPTICS>THERMAL RADIATION>Q 5.263.
A short light pulse of energy E=7.5 J falls in the form of a narrow and almost parallel beam on a mirror plate, whose reflection coefficient is ρ=0.60. The angle of incidence is 30°. In terms of the corpuscular theory, find the momentum transferred to the plate. Speed of light c=3×108 ms-1.
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Problems in General Physics>Chapter 5 - OPTICS>THERMAL RADIATION>Q 5.264.
A plane light wave of intensity I=0.20 W cm-2, falls on a plane mirror surface with a reflection coefficient ρ=0.8. The angle of incidence is 45°. In terms of the corpuscular theory, find the magnitude of the normal pressure exerted by light on that surface. Speed of light, c=3×108 ms-1.