Find eyepiece of the astronomical telescope with focal length f.

Content Curator

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

CBSE CLASS XII Related Questions

1.
Two air-filled capacitors of capacitances $C_1$ and $C_2$ are connected in parallel with a dc battery. After the capacitors are fully charged, a slab of dielectric constant K is inserted between the plates of each capacitor. How will the (i) charge on each capacitor and (ii) energy stored in the capacitor affected after the slab is introduced.

View Solution

2.
An electric field $\vec{E}$ is established across the ends of a cylindrical conductor of length L and area of cross-section A. Discuss how electrons attain an average velocity, independent of time. Hence, obtain a relation between current in the conductor and this ‘average velocity’ of electrons.

View Solution

3.
Read the following paragraph and answer the questions that follow.
A p-type or n-type semiconductor can be converted into a p-n junction by doping it with suitable impurity. The motion of majority charge carriers causes diffusion current across the junction while the barrier electric field causes motion of minority carriers for drift current. In case of unbiased diode, the diffusion and drift currents are equal. This equilibrium is disturbed by the biasing batteries. Diodes, therefore, allow currents in one direction. This property of diode is used in making rectifiers.

4.
If T is the time period of the rotation of the coil, at what values of t in a cycle, the emf generator is maximum ?

View Solution

5.
A student sets up the circuit as shown in the figure to find the value of unknown resistance X and records a set of readings of the voltmeter and the ammeter by using the rheostat.

6.
Two copper wires having their radii in the ratio of 3 : 2 are connected in series across a battery. Find the ratio of the drift velocities of the electrons in the wires.

View Solution

Find eyepiece of the astronomical telescope with focal length f.

CBSE CLASS XII Related Questions

4.
If T is the time period of the rotation of the coil, at what values of t in a cycle, the emf generator is maximum ?

5.
A student sets up the circuit as shown in the figure to find the value of unknown resistance X and records a set of readings of the voltmeter and the ammeter by using the rheostat.

6.
Two copper wires having their radii in the ratio of 3 : 2 are connected in series across a battery. Find the ratio of the drift velocities of the electrons in the wires.

Comments

SUBSCRIBE TO OUR NEWS LETTER

Find eyepiece of the astronomical telescope with focal length f.

CBSE CLASS XII Related Questions

4.If T is the time period of the rotation of the coil, at what values of t in a cycle, the emf generator is maximum ?

5.A student sets up the circuit as shown in the figure to find the value of unknown resistance X and records a set of readings of the voltmeter and the ammeter by using the rheostat.

6.Two copper wires having their radii in the ratio of 3 : 2 are connected in series across a battery. Find the ratio of the drift velocities of the electrons in the wires.

Comments

SUBSCRIBE TO OUR NEWS LETTER

4.
If T is the time period of the rotation of the coil, at what values of t in a cycle, the emf generator is maximum ?

5.
A student sets up the circuit as shown in the figure to find the value of unknown resistance X and records a set of readings of the voltmeter and the ammeter by using the rheostat.

6.
Two copper wires having their radii in the ratio of 3 : 2 are connected in series across a battery. Find the ratio of the drift velocities of the electrons in the wires.