Question 1

In a telescope,to what does the term aberration refer?
A) the absorption of light by the glass in the lenses
B) the magnifying power of the telescope
C) the fundamental limitation of any telescope to resolve very small details in the image
D) a defect in design that blurs or distorts the image

Accepted Answer

Aberration refers to a defect in design that blurs or distorts the image in a telescope. This can be caused by various factors such as limitations in the shape and position of lenses or mirrors, as well as atmospheric interference.

Question 2

Chromatic aberration occurs in a refracting telescope when:
A) the different colors of light do not focus at the same point.
B) some wavelengths are scattered out of the telescope by imperfections in the glass in the lenses or are reflected back by the front surface of the lens.
C) the lenses bend under their own weight, distorting the final image.
D) light from some wavelengths is absorbed by the lenses, distorting the colors of objects.

Accepted Answer

Chromatic aberration occurs when different colors of light bend differently as they pass through a lens, causing them to focus at slightly different points. This results in a blurry and distorted image with a colored fringe around objects.

Question 3

Light from each part of the source being observed falls on each part of the primary mirror of a Newtonian telescope not obstructed by the secondary mirror.The important consequence of this is that:
A) the image does not have a dark spot indicating the presence of the secondary mirror.
B) the image is not darkened (overall) because of the presence of the secondary mirror.
C) cheaper spherical mirrors can be used rather than a more costly parabolic mirror.
D) the secondary mirror can be made as large as needed without influencing the quality of the image.

Accepted Answer

Since the light from each part of the source falls on each part of the primary mirror, it means that none of the parts are hindered or obstructed by the presence of the secondary mirror. This leads to the absence of any dark spots in the image, indicating the absence of the secondary mirror in the line of sight.

Question 4

When visible light passes through a glass prism or a glass lens,which wavelengths of light are deflected most by the glass? (See Figures 3-1 and 3-20a,Comins,Discovering the Essential Universe,6th ed.)
A) the longer wavelengths
B) The light is not deflected by glass because glass is transparent.
C) All wavelengths have their directions changed by the same amount.
D) the shorter wavelengths

Accepted Answer

The shorter wavelengths of light are deflected more by the glass, causing the phenomenon of dispersion where different colors of light are separated. This is what causes a rainbow when sunlight passes through raindrops, which act like tiny prisms.

Question 5

A department store sells an "astronomical telescope" with an objective lens of 30-cm focal length and a diameter of 5 cm,and an eyepiece lens of focal length 5 mm and diameter 4 mm.What is the magnifying power of this telescope?
A) 6 times
B) 150 times
C) 60 times
D) 12.5 times

Accepted Answer

The magnifying power of a telescope is given by the formula:

Magnifying power = focal length of objective lens / focal length of eyepiece lens

Substituting the given values:

Magnifying power = 30 cm / 5 mm

Converting both values to the same units (millimeters):

Magnifying power = 300 mm / 5 mm = 60

Therefore, the magnifying power of this telescope is 60 times.

Question 6

The largest refracting telescope in the world is the 102-cm (40-inch)telescope at Yerkes Observatory,built in 1897.Why have no larger refracting telescopes ever been built?
A) Larger lenses would have too much chromatic aberration.
B) The sagging of larger lenses under their own weight would produce image distortion.
C) The thickness of larger lenses would produce too much spherical aberration.
D) Larger lenses would produce too much magnification.

Accepted Answer

The sagging of larger lenses under their own weight would produce image distortion, which would limit the image quality and decrease the usefulness of the telescope. This issue is particularly problematic for refracting telescopes, which rely on a single large lens, and cannot be easily corrected with additional lenses or mirrors. As a result, most modern telescopes use reflecting designs, where the weight of the mirror is supported from behind and does not cause distortion.

Question 7

What is chromatic aberration in a telescope?
A) Light of different colors reflecting from the objective mirror of the telescope comes to a focus at different points in front of the mirror.
B) Light of different colors comes to a focus at different points behind the objective lens inside the telescope.
C) Light striking the lens at different distances from the center of the lens comes to a focus at different points inside the telescope.
D) The objective lens varies in thickness from center to edge, and light passing through the different thicknesses suffers different amounts of absorption, thereby coloring the image.

Accepted Answer

Chromatic aberration in a telescope occurs when light of different colors comes to a focus at different points behind the objective lens inside the telescope. This results in a blurry, color-fringed image. This can be corrected using a combination of lenses of different materials with different refractive indices, known as achromatic lenses.

Question 8

A refracting telescope has an objective lens of focal length 40 cm and a diameter of 10 cm,and an eyepiece of focal length 5 cm and diameter 1 cm.What is the magnifying power of this telescope?
A) 10 times
B) 40 times
C) 2 times
D) 8 times

Accepted Answer

The magnifying power of a refracting telescope is given by the formula: Magnifying Power = Focal Length of Objective Lens / Focal Length of Eyepiece. Here, it is 40 cm / 5 cm = 8 times.

Question 9

Chromatic aberration is the failure of a telescope objective to bring all colors of light to the same focus and appears in:
A) only a reflecting telescope.
B) both reflecting and refracting telescopes.
C) all telescopes because it is caused by a basic property of light.
D) only a refracting telescope.

Accepted Answer

Chromatic aberration is a common problem for refracting telescopes because the objective lens they use bends different colors of light at slightly different angles, causing them to focus at different points. Reflector telescopes are not affected by chromatic aberration because they use mirrors instead of lenses to focus light.

Question 10

What is the reason for the fact that a reflecting telescope used at prime focus does NOT suffer from chromatic aberration?
A) The aluminum coating on the mirror absorbs light from all wavelengths, except the one of interest to the astronomer, and this light is focused perfectly.
B) The light has passed through only one lens.
C) All wavelengths of light are reflected by the same amount regardless of color.
D) The lens is so perfectly formed that all colors of light travel through the lens along the same path.

Accepted Answer

Reflecting telescopes use mirrors, which reflect all wavelengths of light equally, preventing chromatic aberration that occurs in lenses when different colors are refracted by different amounts.

Question 11

How is spherical aberration usually overcome in the objective lens of a refracting astronomical telescope?
A) by making the lens very thin, with a long focal length
B) by coating the lenses with an antireflective coating
C) by grinding the lens surfaces to a parabolic shape
D) by using a filter that allows only a small range of wavelengths (colors) through the telescope

Accepted Answer

The answer of How is spherical aberration usually overcome in...

Question 12

How is chromatic aberration MOST often corrected in a modern refracting telescope?
A) by using a combination of two lenses made from different types of glass
B) by painting the inside of the telescope jet black to minimize reflections
C) by grinding the lens surfaces into a parabolic shape
D) by using a prism to recombine the colors into white light

Accepted Answer

Chromatic aberration is corrected by using a combination of two lenses made from different types of glass. This is known as an achromatic lens. The two types of glass used have different refractive indices, which helps to reduce the dispersion of light and bring all colors to a common focus point.

Question 13

A small refracting "spyglass" telescope has an objective with a focal length of about 30 inches.The world's largest refracting telescope at Yerkes Observatory has an objective with a focal length of 63.5 feet.If they both use the same eyepiece,how much larger is the image with Yerkes than with the spyglass?
A) about twice
B) about 16 times
C) about 25 times
D) about 625 times

Accepted Answer

The ratio of the size of the image produced by the Yerkes telescope to the size of the image produced by the spyglass telescope can be found using the formula:

size of image ∝ focal length of objective

Since they use the same eyepiece, the size of the image is proportional to the focal length of the objective.

Therefore,

size of image with Yerkes telescope / size of image with spyglass telescope = focal length of Yerkes objective / focal length of spyglass objective

Substituting the given values, we get:

size of image with Yerkes telescope / size of image with spyglass telescope = 63.5 feet / 30 inches

= (63.5 x 12) inches / 30 inches

= 25.4 inches / inch

So, the size of the image produced by the Yerkes telescope is about 25 times larger than the size of the image produced by the spyglass telescope.

Therefore, the correct answer is (C) about 25 times.

Question 14

A small refracting "spyglass" telescope has an objective lens with a diameter of 2 inches.The world's largest refracting telescope at Yerkes Observatory has an objective lens with a diameter of 40 inches.Assuming that all light striking the objectives passes through them,how much larger is the light-gathering power of Yerkes than that of the spyglass?
A) twice
B) 40 times
C) 80 times
D) 400 times

Accepted Answer

The amount of light gathered by a telescope depends on the area of its objective lens. The area of the objective lens of the spyglass is pi(1^2) = pi square inches, while the area of the Yerkes telescope's objective lens is pi(20^2) = 400pi square inches. Therefore, the light-gathering power of Yerkes is (400pi)/(pi) = 400 times larger than that of the spyglass. Hence, the correct answer is D, 400 times.

Question 15

How far apart should the objective lens and the eyepiece lens be in a refracting telescope? (See Figure 3-19,Comins,Discovering the Essential Universe,6th ed.)
A) a distance equal to the focal length of the objective lens
B) a distance equal to the focal length of the eyepiece lens
C) a distance equal to the focal length of the objective lens minus the focal length of the eyepiece lens
D) a distance equal to the sum of the focal lengths of the two lenses

Accepted Answer

In a refracting telescope, the objective lens and the eyepiece lens should be separated by a distance equal to the sum of their focal lengths to properly focus the image.

Question 16

What causes chromatic aberration in the objective lens of a telescope?
A) Reflection of light back and forth inside the lens produces multiple images, and the overall combination of the images will be distorted.
B) Different colors are refracted through different angles at each surface of the lens.
C) Different colors suffer different amounts of absorption by the glass in the lens.
D) The shape of the lens surface distorts the image.

Accepted Answer

Chromatic aberration is caused by different colors being refracted through different angles at each surface of the lens, leading to the colors not converging at the same point and creating a distorted image.

Question 17

Chromatic aberration,the inability of a simple lens to focus all colors of light to the same focal point,is reduced in astronomical telescopes by:
A) adding a carefully shaped mirror to the lens to produce a lens-mirror combination.
B) combining two lenses of different shape, made from the same kind of glass.
C) bending the lens in its mounting.
D) combining two lenses of different shape, made from different kinds of glass.

Accepted Answer

Combining two lenses of different shape, made from different kinds of glass is the preferred method to reduce chromatic aberration as it allows for the correction of different wavelengths of light passing through the lens. This technique is known as apochromatic correction and is commonly used in modern astronomical telescopes.

Question 18

Which of the following types of telescopes is MOST seriously affected by chromatic aberration?
A) radio
B) refracting
C) Newtonian
D) Cassegrain

Accepted Answer

Refracting telescopes are most seriously affected by chromatic aberration due to the way light is refracted and dispersed by the lens elements.

Question 19

A lens with spherical surfaces suffers from spherical aberration because:
A) the lens sags under its own weight, distorting the image.
B) the starlight is distorted by turbulence in Earth's atmosphere.
C) different colors are focused at different distances from the lens.
D) different parts of the lens focus the light at different distances from the lens.

Accepted Answer

Spherical aberration occurs in a lens with spherical surfaces because different parts of the lens bend and focus light at different distances from the lens, causing the image to be blurred or distorted.

Question 20

Spherical aberration occurs in a lens when it is:
A) not spherical enough.
B) not exactly the same shape on each side.
C) spherical.
D) parabolic.

Accepted Answer

Spherical aberration occurs in a lens when it is spherical. This type of aberration happens because rays that pass through the edge of a spherical lens are not focused at the same point as rays that pass through the center. This is due to the geometric shape of the lens.

Quiz 3: Light and Telescopes

In a telescope,to what does the term aberration refer?

Chromatic aberration occurs in a refracting telescope when:

Light from each part of the source being observed falls on each part of the primary mirror of a Newtonian telescope not obstructed by the secondary mirror.The important consequence of this is that:

When visible light passes through a glass prism or a glass lens,which wavelengths of light are deflected most by the glass? (See Figures 3-1 and 3-20a,Comins,Discovering the Essential Universe,6th ed.)

A department store sells an "astronomical telescope" with an objective lens of 30-cm focal length and a diameter of 5 cm,and an eyepiece lens of focal length 5 mm and diameter 4 mm.What is the magnifying power of this telescope?

The largest refracting telescope in the world is the 102-cm (40-inch) telescope at Yerkes Observatory,built in 1897.Why have no larger refracting telescopes ever been built?

What is chromatic aberration in a telescope?

A refracting telescope has an objective lens of focal length 40 cm and a diameter of 10 cm,and an eyepiece of focal length 5 cm and diameter 1 cm.What is the magnifying power of this telescope?

Chromatic aberration is the failure of a telescope objective to bring all colors of light to the same focus and appears in:

What is the reason for the fact that a reflecting telescope used at prime focus does NOT suffer from chromatic aberration?

How is spherical aberration usually overcome in the objective lens of a refracting astronomical telescope?

How is chromatic aberration MOST often corrected in a modern refracting telescope?

How far apart should the objective lens and the eyepiece lens be in a refracting telescope? (See Figure 3-19,Comins,Discovering the Essential Universe,6th ed.)

What causes chromatic aberration in the objective lens of a telescope?

Chromatic aberration,the inability of a simple lens to focus all colors of light to the same focal point,is reduced in astronomical telescopes by:

Which of the following types of telescopes is MOST seriously affected by chromatic aberration?

A lens with spherical surfaces suffers from spherical aberration because:

Spherical aberration occurs in a lens when it is: