Telescope Refracting and Reflecting - UNSOLVED PRACTICE SET
Chapter: Ray Optics and Optical Instruments | Topic: Telescope Refracting and Reflecting
TELESCOPE REFRACTING AND REFLECTING - UNSOLVED PRACTICE SET
Topic: Telescope Refracting and Reflecting
Multiple Choice Questions
Q1. In an astronomical telescope, the objective lens has:
- Small focal length and large aperture
- Large focal length and large aperture
- Small focal length and small aperture
- Large focal length and small aperture
Q2. The magnifying power of an astronomical telescope when the final image is formed at infinity is:
- M = fₑ/f₀
- M = f₀/fₑ
- M = f₀ + fₑ
- M = f₀ × fₑ
Q3. In a terrestrial telescope, an additional lens is used to:
- Increase magnification
- Make the final image erect
- Decrease the length of the telescope
- Increase the aperture
Q4. Reflecting telescopes are preferred over refracting telescopes because:
- They are cheaper to make for large apertures
- They do not suffer from chromatic aberration
- Both (a) and (b)
- They have higher magnifying power
Q5. The resolving power of a telescope depends on:
- The focal length of the objective
- The diameter (aperture) of the objective
- The focal length of the eyepiece
- The length of the telescope tube
Q6. In a Newtonian reflecting telescope, the image is viewed using:
- A convex lens
- A concave mirror and a plane mirror
- A convex mirror
- A prism
Short Answer Questions
Q7. What is the difference between an astronomical telescope and a terrestrial telescope?
Q8. Why does an astronomical telescope produce an inverted image? Is this a disadvantage for astronomical observations?
Q9. What is the advantage of a reflecting telescope over a refracting telescope? Name two famous reflecting telescopes.
Q10. The magnifying power of a telescope is 20. If the focal length of the objective is 100 cm, calculate the focal length of the eyepiece.
Q11. Why is the aperture of the objective lens of a telescope made as large as possible?
Q12. What is the normal adjustment of a telescope? Why is it preferred for viewing distant objects?
Long Answer Questions
Q13. With the help of a ray diagram, explain the construction and working of an astronomical telescope in normal adjustment. Derive the expression for its magnifying power.
Q14. Describe the construction and working of a reflecting telescope (Newtonian type). Explain why reflecting telescopes are preferred for large astronomical observations.
Q15. Compare refracting and reflecting telescopes under the following heads:
(i) Construction
(ii) Image quality
(iii) Chromatic aberration
(iv) Suitability for large apertures
(v) Maintenance
Numerical & Application-Based Problems
Q16. An astronomical telescope has an objective of focal length 150 cm and an eyepiece of focal length 5 cm.
(a) Calculate the magnifying power in normal adjustment.
(b) Calculate the length of the telescope in normal adjustment.
(c) Calculate the magnifying power when the final image is formed at the near point (25 cm).
(d) Calculate the length of the telescope in this case.
Q17. A reflecting telescope has a concave mirror of focal length 200 cm as the objective and a convex lens of focal length 5 cm as the eyepiece.
(a) Calculate the magnifying power in normal adjustment.
(b) Calculate the diameter of the image of the moon formed by the objective if the moon subtends an angle of 0.5° at the objective.
(c) If the aperture of the objective mirror is 20 cm, calculate its resolving power for light of wavelength 550 nm.
Q18. In your school's astronomy club, students are building a simple refracting telescope for sky gazing.
(a) They use an objective lens of focal length 80 cm and an eyepiece of focal length 4 cm. Calculate the magnifying power and the length of the telescope in normal adjustment.
(b) During a session, they observe Jupiter and its moons. Jupiter subtends an angle of 0.01° at the telescope. Calculate the angle subtended by Jupiter's image at the eye.
(c) A student suggests using a more powerful eyepiece of focal length 1 cm to get higher magnification. Discuss the advantages and disadvantages of this suggestion.
(d) The Vainu Bappu Observatory in Tamil Nadu has a telescope with an objective mirror of diameter 2.3 m. Calculate its resolving power for light of wavelength 500 nm and explain why such a large aperture is necessary for astronomical observations.
(e) Explain why radio telescopes like the Giant Metrewave Radio Telescope (GMRT) near Pune need to be much larger than optical telescopes to achieve comparable resolution.