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?
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
Draw a labeled ray diagram to obtain the real image formed by an astronomical telescope in normal adjustment position. Define its magnifying power.
- 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?
Draw a ray diagram depicting the formation of the image by an astronomical telescope in normal adjustment.
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
Write the two important factors considered to increase the magnifying power?
"A telescope resolves whereas a microscope magnifies." Justify this statement ?
Write two important limitations of a refracting telescope over a reflecting-type telescope.
Define magnifying power of a telescope. Write its expression.
Draw a labeled ray diagram of a reflecting telescope. Mention its two advantages over the refracting telescope.
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?
(i) What is meant by resolving power of a telescope?
(ii) State any one method of increasing the resolving power of an astronomical telescope.
Draw a labelled ray diagram showing the formation of an image by a refracting telescope when the final image lies at infinity.
Define the term 'resolving power of a telescope'. How will the resolving power be effected with the increase in
(i) Wavelength of light used.
(ii) Diameter of the objective lens.
Draw a labelled ray diagram showing the image formation by a refracting telescope. Define its magnifying power.
In an astronomical telescope in normal adjustment, a straight black line of length L is drawn on the objective lens. The eyepiece forms a real image of this line whose length is 𝑙. What is the angular magnification of the telescope?
