Find eyepiece of the astronomical telescope with focal length f.

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Question: An astronomical telescope and a Galilean telescope use identical objective lenses. They have the same magnification when both are in normal adjustment. The eyepiece of the astronomical telescope has a focal length ‘f’.

Let's call the focal length of the eyepiece of the Galilean telescope "g". Then, we know that the magnification (M) of both telescopes is the same, which means:

M = - f_o / f_e for the Galilean telescope
M = f_o / f_e for the astronomical telescope

where f_o is the focal length of the objective lens and f_e is the effective focal length of the telescope. The negative sign in the equation for the Galilean telescope is because the image is inverted.

Since M is the same for both telescopes, we can set the two equations equal to each other and solve for g:

f_o / fe_g = fo / f
fe_g = -f

So, the effective focal length of the Galilean telescope is -f. This means that the eyepiece must have a negative focal length, which is why the Galilean telescope has a concave eyepiece.

Now, we will apply a formula to find eyepiece of astronomical telescope with focal length f which is given as:

L= f_o + f_e+ d

Where, L= Length

f_o = Focal length of objective lens

f_e= Focal length of eyepiece

d= Final image distance formation by eyepiece lens

Note: The final image distance (d) is always taken as +25 cm in a normal adjustment.

Also check:

Important Learning Concepts
Biconvex Lens	Telescope	Luminance
Snell’s Law Formula	NCERT Solutions of Light	Dispersion of Light
Refraction at spherical surfaces and lenses	Refraction through a prism	Transmission, Absorption and Reflection of Light

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Find eyepiece of the astronomical telescope with focal length f.

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This ‘average velocity’ is found be few mm/s for currents in range of a few amperes. How then is current established almost the instant a circuit is closed ?

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Find eyepiece of the astronomical telescope with focal length f.

CBSE CLASS XII Related Questions

4.This ‘average velocity’ is found be few mm/s for currents in range of a few amperes. How then is current established almost the instant a circuit is closed ?

Comments

SUBSCRIBE TO OUR NEWS LETTER

4.
This ‘average velocity’ is found be few mm/s for currents in range of a few amperes. How then is current established almost the instant a circuit is closed ?