Advertisements
Advertisements
प्रश्न
A lady cannot see objects closer than 40 cm from the left eye and closer than 100 cm from the right eye. While on a mountaineering trip, she is lost from her team. She tries to make an astronomical telescope from her reading glasses to look for her teammates. (a) Which glass should she use as the eyepiece? (b) What magnification can she get with relaxed eye?
Advertisements
उत्तर
Given:
For the left glass lens of the lady, we have:
v = – 40 cm and u = – 25 cm
The lens formula is given by
`1/v -1/u =1/f`
Putting the values, we get:
`1/f = 1/((-40)) - 1/((-25)) = 3/200`
`=> f = 200/3 = 66.6` cm
For the right glass lens of the lady, we have:
v = – 100 cm, u = – 25 cm
The lens formula is given by
`1/v -1/u =1/f`
Putting the values, we get:
`1/f = 1/((-100)) - 1/((-25)) =3/100`
`=> f = 100/3 = 33.3 cm `
(a) An astronomical telescope consists of two lenses: the objective lens having a large focal length and the eyepiece lens having a smaller focal length. So, she should use the right lens of focal length 33.3 cm as the eyepiece lens.
(b) With relaxed eye in normal adjustment,
f0 = 66.6 cm and fe = 33.3 cm
Magnification (m) in normal adjustment is given by
`m =f_0/f_e`
∴ m =`(66.6 text/"cm") /(33.3 text/" cm")` = 2
So, with the relaxed eye, she can get the magnification of 2.
APPEARS IN
संबंधित प्रश्न
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?
You are given the following three lenses. Which two lenses will you use as an eyepiece and as an objective to construct an astronomical telescope ? Give reason
| Lenses | Power (D) | Aperture (cm) |
| L1 | 3 | 8 |
| L2 | 6 | 1 |
| L3 | 10 | 1 |
Write two important advantages of reflecting telescope over a refracting telescope.
Draw a labelled ray diagram of an image formed by a refracting telescope with the final image formed at infinity. Derive an expression for its magnifying power with the final image at infinity
With regard to an astronomical telescope of refracting type~ state how you will increase its:
1) magnifying power
2) resolving power
State the condition under which a large magnification can be achieved in an astronomical telescope.
Describe briefly the two main limitations and explain how far these can be minimized in a reflecting telescope ?
Draw a labelled ray diagram of an astronomical telescope to show the image formation of a distant object. Write the main considerations required in selecting the objective and eyepiece lenses in order to have large magnifying power and high resolution of the telescope.
How is the working of a telescope different from that of a microscope?
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?
An astronomical telescope uses two lenses of powers 10 dioptres and 1 dioptre. If the final image of a distant object is formed at infinity, calculate the length of the telescope
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.
Define the term ‘resolving power of a telescope’.
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).
With the help of a ray diagram explain the working of a reflecting telescope.
Draw a labelled ray diagram showing the image formation by a refracting telescope. Define its magnifying power.
The magnifying power of an astronomical telescope in normal adjustment is 2.9 and the objective and the eyepiece are separated by a distance of 150 cm. Find the focal lengths of the two lenses.
