An astronomical telescope has an objective of focal length 200 cm and ...
Given:
- Focal length of the objective lens, f1 = 200 cm
- Focal length of the eyepiece, f2 = 10 cm
- Distance of the screen from the eyepiece, d = 40 cm
- Diameter of the sun's image on the screen, Dimage = 6 cm
- Average Earth-Sun distance, DES = 1.5 × 10^11 m
To Find:
- Diameter of the sun, Dsun
Formula:
The angular magnification of a telescope is given by:
M = -f1/f2
The angular magnification can also be expressed as the ratio of the apparent angular diameter of the image to the actual angular diameter of the object:
M = θimage/θsun
The actual angular diameter of the sun, θsun = Dsun/DES
The apparent angular diameter of the sun, θimage = Dimage/d
Calculation:
- Given that the distance between the objective and the eyepiece is adjusted to obtain the image on the screen, it implies that the final image is formed at the least distance of distinct vision (25 cm).
Using the formula for the angular magnification of the telescope, we have:
M = -f1/f2
=> M = -200 cm/10 cm
=> M = -20
Using the formula for the ratio of the apparent angular diameter to the actual angular diameter, we have:
M = θimage/θsun
=> -20 = (6 cm/40 cm) / θsun
=> -20 = 0.15 / θsun
=> θsun = -0.15/20
=> θsun = -0.0075 radians
The negative sign indicates that the image formed is inverted.
Using the formula for the actual angular diameter of the sun, we have:
θsun = Dsun/DES
=> -0.0075 radians = Dsun / (1.5 × 10^11 m)
=> Dsun = -0.0075 radians × (1.5 × 10^11 m)
=> Dsun = -1.125 × 10^9 radians × m
Answer:
The diameter of the sun is approximately 1.125 × 10^9 radians × meters.
An astronomical telescope has an objective of focal length 200 cm and ...
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