Advertisements
Advertisements
Questions
Draw a ray diagram of a refracting astronomical telescope when final image is formed at infinity. Also write the expression for its angular magnification (magnifying power).
Draw a labelled ray diagram of an astronomical telescope when the final image is formed at infinity. Write the expression for its magnifying power.
Advertisements
Solution
In an astronomical telescope, the objective lens forms an intermediate real image, and the eyepiece lens magnifies it.
- The object (e.g., a distant star) is placed far away, so the incoming rays are parallel.
- These parallel rays first pass through the objective lens, which converges them to form a real, inverted image at its focal point (Fo).
- The eyepiece lens is then positioned such that this intermediate image lies at its focal point. As the eyepiece lens diverges the rays, they appear to originate from infinity, creating the final image that is seen by the observer.
Magnifying power (Angular Magnification):
1. When the image is formed at a finite distance (e.g., at distance D):
The magnifying power is given by the formula:
M = `- f_o/f_e (1 + f_e/D)`
This formula takes into account the image formed at a distance D (closer than infinity).
2. When the image is formed at infinity (which is typical for astronomical telescopes):
The magnifying power simplifies to:
M = `- f_o/f_e`
This is the standard expression for magnifying power when the final image is at infinity.
RELATED QUESTIONS
A small telescope has an objective lens of focal length 144 cm and an eyepiece of focal length 6.0 cm. What is the magnifying power of the telescope? What is the separation between the objective and the eyepiece?
- A giant refracting telescope at an observatory has an objective lens of focal length 15 m. If an eyepiece of focal length 1.0 cm is used, what is the angular magnification of the telescope?
- If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens? The diameter of the moon is 3.48 × 106 m, and the radius of lunar orbit is 3.8 × 108 m.
- For the telescope is in normal adjustment (i.e., when the final image is at infinity)? what is the separation between the objective lens and the eyepiece?
- If this telescope is used to view a 100 m tall tower 3 km away, what is the height of the image of the tower formed by the objective lens?
- What is the height of the final image of the tower if it is formed at 25 cm?
You are given three lenses of power 0.5 D, 4 D, and 10 D to design a telescope.
1) Which lenses should be used as objective and eyepiece? Justify your answer.
2) Why is the aperture of the objective preferred to be large?
With regard to an astronomical telescope of refracting type~ state how you will increase its:
1) magnifying power
2) resolving power
A giant refracting telescope at an observatory has an objective lens of focal length 15 m. If an eyepiece lens of focal length 1.0 cm is used, find the angular magnification of the telescope. If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens? The diameter of the moon is 3.42 × 106 m and the radius of the lunar orbit is 3.8 × 108 m.
A Galilean telescope is 27 cm long when focussed to form an image at infinity. If the objective has a focal length of 30 cm, what is the focal length of the eyepiece?
Draw a labelled ray diagram showing the formation of an image by a refracting telescope when the final image lies at infinity.
Draw a labelled ray diagram of an astronomical telescope in the near point adjustment position. A giant refracting telescope at an observatory has an objective lens of focal length 15 m and an eyepiece of focal length 1.0 cm. If this telescope is used to view the Moon, find the diameter of the image of the Moon formed by the objective lens. The diameter of the Moon is `3.48 xx 10^6`m, and the radius of the lunar orbit is `3.48 xx 10^8`m.
Draw a labelled ray diagram showing the image formation by a refracting telescope. Define its magnifying power.
