A small Keplerian telescope has an objective with a 1.33 m focal length. Its eyepiece is a 2.82 cm focal length lens. It is used to look at a 25000 km diameter sunspot on the sun, a distance 1.5*108 km from Earth.

Required:
What angle is subtended by the sunspot's telescopic image in degree?

Respuesta :

Answer:

The angle is  [tex]\phi = 0.45 0 ^o[/tex]

Explanation:

From the question we are told that  

     The objective  focal length   [tex]f = 1.33 \ m[/tex]

     The  eyepiece focal length is  [tex]f_o = 2.82 \ cm = 0.0282 \ m[/tex]

      The diameter of the sunlight is  [tex]d = 25000km = 2.5 *10^{7} \ m[/tex]

       The distance of the sun from from the earth is  [tex]D = 1.5 *10^8 km = 1.5 *10^{11} \ m[/tex]

  Generally the magnification of the object is mathematically evaluated as

        [tex]m = -\frac{f_o }{f_e }[/tex]

The negative  sign is because the lens of the telescope is  diverging light

 substituting values  

      [tex]m = -\frac{1.33 }{0.0282 }[/tex]

      [tex]m = - 47.16 3[/tex]

Now we can obtain the angle made by the object (sunlight ) with respect to the telescope  as follows  

        [tex]tan \theta = \frac{d}{D}[/tex]

substituting values

      [tex]tan \theta = \frac{2.5 *10^{7}}{1.5*10^{11}}[/tex]

      [tex]tan \theta = 0.0001667[/tex]

      [tex]\theta= tan^{-1}[0.0001667][/tex]

     [tex]\theta= 0.00955^o[/tex]

The  magnification can  also be mathematically represented as

      [tex]m = \frac{\phi }{\theta }[/tex]

Where [tex]\phi[/tex] is the angle the image made with telescope

Since the negative sign indicate direction of light movement we will remove it from the calculation below

      =>   [tex]47.163 = \frac{\phi}{0.00955}[/tex]

     =>    [tex]\phi = 0.45 0 ^o[/tex]

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