Advertisements
Advertisements
рдкреНрд░рд╢реНрди
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 ЁЭСЩ. What is the angular magnification of the telescope?
Advertisements
рдЙрддреНрддрд░
Let fo and fe be the focal length of the objective and eyepiece respectively.
For normal adjustment, the distance from the objective to the eyepiece is fo + fe.
Taking the line on the objective as an object and the eyepiece as a lens.
u = -(fo + fe) and f = fe
`1/v = 1/([-{f_o + f_e}]) = 1/f_e` ⇒ v = `((f_o + f_e)/f_o)f_e`
Linear magnification (eyepiece) = `v/u = "Image size"/"Object size" = f_e/f_o = l/L`
∴ Angular magnification of the telescope
M = `f_o/f_e = L/l`
APPEARS IN
рд╕рдВрдмрдВрдзрд┐рдд рдкреНрд░рд╢реНрди
Draw a labeled ray diagram to obtain the real image formed by an astronomical telescope in normal adjustment position. Define its magnifying power.
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 |
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
Describe briefly the two main limitations and explain how far these can be minimized in a reflecting telescope ?
Define magnifying power of a telescope. Write its expression.
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 ray diagram of a refracting astronomical telescope when final image is formed at infinity. Also write the expression for its angular magnification (magnifying power).
A small telescope has an objective lens of focal length 140 cm and an eyepiece of focal length 5.0 cm. Find the magnifying power of the telescope for viewing distant objects when
- the telescope is in normal adjustment,
- the final image is formed at the least distance of distinct vision.
Draw a ray diagram of astronomical telescope for the final image formed at infinity.
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.
