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In this lesson, we will learn how to describe the effect of wavelength on the limit of resolution and how to describe the effects of diffraction from circular apertures.
The headlights of a car are 1.3 m apart.
What is the maximum distance at which an eye with a pupil diameter of 0.40 cm
can resolve these two headlights? Assume that the wavelength of light from the headlights is
The primary mirror of the orbiting Hubble Space Telescope has an angular resolution
. What is the smallest detail that it can observe at a distance of
The 8.1-m-diameter Gemini North telescope at Mauna Kea, Hawaii, observes two objects on the Moon.
What is the minimum distance on the lunar surface that the objects must be separated by for them to be resolvable?
Assume that only the diffraction effects of the telescope aperture limit the resolution and that
550 nm wavelength
light is used to observe the objects.
m as the distance to the Moon.
Quasars, or quasi-stellar radio sources, are astronomical objects discovered in 1960.
They are distant but strong emitters of radio waves at very small angular sizes.
The quasar 3C405 is actually two discrete radio sources that subtend an angle of 82 arcsec.
If this object is studied using radio emissions at a frequency of
410 MHz, what is the minimum
diameter of a radio telescope that can resolve the two sources?
Light of wavelength 461.9 nm emerges from the 2.0-mm-diameter circular aperture of a krypton ion laser. Due to diffraction, the beam widens as it moves away from the laser.
What is the diameter of the central bright spot produced by this beam 1.0 m away from the laser?
What is the diameter of the central bright spot produced by this beam 1.0 km away from the laser?
What is the diameter of the central bright spot produced by this beam 1000 km away from the laser?
What is the diameter of the central bright spot produced by this beam
km away from the laser?
The limit to the eye’s acuity is actually related to diffraction by the pupil.
Assume that the pupil of an eye is 3.00 mm
in diameter and that light has an average wavelength of
What is the angle between two points of light that are just-resolvable by the eye?
Taking the angle between two points just-resolvable by the eye,
what is the greatest possible distance a car can be from an eye if the eye can resolve the
car’s two headlights, given that the headlights are 1.30 m apart?
What is the distance between two just-resolvable points held at a distance of 0.800 m from an eye?
The characters of a stadium scoreboard are formed with closely spaced lightbulbs that radiate primarily yellow light of wavelength
m. Determine how closely the bulbs must be spaced so that an observer 80.0 m away sees a display of continuous lines rather than the individual bulbs. Use a value of 5.0 mm for the pupil diameter of the observer’s eye.
A Helium-Neon laser beam has a wavelength of 633 nm.
What is the minimum angular spread of the beam?
What is the diameter of an illuminated spot that this beam would create on a surface 15.0 km away from its source?
What is the diameter of an illuminated spot that this beam would create on a surface at a distance of
km from the source?
You are looking down at a highway from inside an aeroplane flying at an altitude of
and you can just distinguish between two individual cars that are very close together on the ground.
How far apart must the two cars be? Assume that the
light from the cars has a wavelength of 550 nm
and that the diameter of your pupils is
A spy satellite orbits Earth at a height of
180 km. What
is the minimum diameter of the objective lens in a telescope
that must be used to resolve columns of troops marching
2.0 m apart?
A 295 m diameter radio telescope detects
radio waves with a 5.00 cm average
wavelength. The telescope just resolves two very distant objects.
What is the angle between the two very distant objects?
What is the minimum separation of these two very distant objects if they are
1.80 million light years distant from the
telescope? Consider the objects to be point sources.
Find the minimum angular spreading of a 630 nm average wavelength flashlight beam that is
originally 4.63 cm in diameter.
Find the minimum diameter mirror on a telescope that would allow you to see details as
small as 500 m on the Moon. Use a value of 384 000 km for the distance to the Moon. Assume an
average wavelength of 550 nm for the light received.
What is the minimum angular separation of two stars that are just resolvable by a
9.30 m diameter telescope, if
atmospheric effects do not limit resolution? Use
570 nm for the wavelength of the
light from the stars.
When dots are placed on a page from a laser printer, they must be close enough so that you
do not see the individual dots of ink. To do this, the separation of the dots must be less
than Raleigh’s criterion. Take the pupil diameter of the eye to be 2.5 mm and the distance
from the paper to the eye to be 50 cm. Find the minimum separation of two dots such that
they cannot be resolved. Take the wavelength of light to be 570 nm.
Two lamps producing light of wavelength
590 nm are fixed
2.00 m apart on a wooden plank. What
is the maximum distance an observer can be from the lamps and still resolve them as two
separate sources of light if the resolution is affected solely by the diffraction of light
entering the eye? Assume light enters the eye through a pupil of diameter
how far apart two objects on the Moon must be to be distinguishable by eye if
only the diffraction effects of the eye’s pupil limit the resolution. Use a
value of 500 nm for the wavelength of light, a value of 4.6 mm for the
pupil diameter, and a value of
km for the distance to the Moon.
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