Question

Draw a labelled ray diagram of a refracting telescope. Define its magnifying power and write the expression for it. Write two important limitations of a refracting telescope over a reflecting type telescope.

Answer 1

Hint: Basically Refracting telescope is meant to focus light. The magnifying power of a telescope is determined by the focal length of the objective. The longer the focal length, the more the magnification is.

Complete step by step solution:
Ray diagram: A ray diagram is used to show the direction that light follows, so that a human can see a point on an object's image. Rays (paths of arrows) for the incident ray and the reflected ray are shown on the diagram.

Refracting telescope: A refracting telescope is a type of optical telescope that utilizes a lens to shape an image as its target. Initially used in spy-glasses and scientific telescopes, the refracting telescope style is now used for long range camera lenses.

Magnifying power: Magnification power is defined as the ratio of image dimensions to object dimensions. The magnification process will take place in the optics, telescopes, microscopes and also in slide projectors. Biconvex are clear magnifying lenses-these lenses are wider at the middle than at the corners.

The mathematical formula for magnifying power is given by,
\[M = \dfrac{{\tan \beta }}{{\tan \alpha }} = \left( {\dfrac{\beta }{\alpha }} \right)\], where \[\alpha \] and \[\beta \] are angle of declination and angle of inclination respectively.
The equation can be also rewritten as,
Magnifying power,
\[\begin{gathered}
  M = \dfrac{{ - {f_{\text{o}}}}}{{{f_e}}} \\
   = \dfrac{{ - {f_{\text{o}}}}}{{{f_e}}}\left( {1 + \dfrac{{{f_e}}}{D}} \right) \\
\end{gathered} \]

Limitation of a refracting telescope over a reflecting type telescope:
Because both ends (with lenses) close the inside of the tube, refracting telescopes do not suffer from debris inside.
Since at both ends the tube is enclosed, refracting telescopes do not have the problem of air blowing about inside the tube, and therefore have clearer, more stable images.

Note: Know the difference between refracting and reflecting type telescope. A refracting telescope is a type of optical telescope that utilizes a lens to shape an image as its target. A reflecting telescope (also known as a reflector) is a telescope using either a single or a mixture of curved mirrors that reflect light and create an image.