Bukhovtsev-et-al-Problems-in-Elementary-Physics

PHYSI CAL OPTICS
157
c
1--------------1---------- B
Fig. 261
791. Prove that a bright spot will be observed at point B
behind circular screen C (Fig. 261) if its dimensions are sufficiently
small.
792. At wha t distance from each other should two men stand
for an eye to distinguish them from a distance of about 11 km?
The resolving power of a normal eye is approximately 1'.
793. A plane light wave (with a length A) is normally incident
on a narrow slit with a width b. Determine the directions
to the illumination minima.
794. Find the optimum dimensions of the aperture in a pin
hole camera depending on the wavelength, Le., the radius,
of the aperture at which a point source will appear on the
camera wall as a circle of minimum diameter, if the distance
from the source of light to the camera is great as compared
with its depth d.
Note. The directions to the illumination minima are determined
in the order of their magnitude by the same formula as
in the case of a slit (see Problem 793), the diameter of the
aperture 2r being used instead of the wid th of the slit b.
795. A monochromatic wave is normally incident on a diffraction
grating with a period of d = 4 X 10- 4 cm. Find the wavelength
A if the angle between the spectra of the second and
third orders is a = 2°30'. The angles of deflection are small.
796. A plane monochromatic wave (At = 5 X 10-& ern) is incident
on a diffraction grating with 500 lines. Determine the maximum
order of the spectrum k that can be observed when the rays
are normally incident on the grating.
797. Find the constant d of a grating that can analyse infrared
radiation with wavelengths up to At = 2 X 10- 1 em. The
radiation is normally incident on the grating.
798. A monochromatic wave is normally incident on a diffraction
grating with a period of d = 4 X 10- 4 em. A lens with a