To determine the resolving power of the telescope Submitted by - roll no 1004,1005,1010,1024,1028

Aim - To determine the resolving power of a telescope. Apparatus required – A telescope, a monochromatic source of light. A microscope and adjustable measuring tape ,an object having two slits separated by a small constant distance

Telescope Adjustable slit Travelling microscope

Theory Theory Resolving power of an instrument is its capacity to see two objects septately which are placed very near each other as separate Also defined ad the reciprocal of the smallest angle subtended at the objective of the telescope by two small objects which can be seen as separate through the telescope. The resolving power of a telescope is given by d/D and the corresponding theoretical value is given by λ/a

Theory or λ/a = d / D Where λ = mean wavelength of light employed, a = width of the rectangular slit for just resolution of two objects, d = separation between two objects, D = distance of the objects from the objective of the telescope This relation also can be used for determination of wavelength of light used

Procedure Mount the telescope on a stand such that its axis lies horizontal and the rectangular lines marked on cardboard or glass on another stand such that they are vertical. Illuminate the lines or the slit with a source of light. Place the telescope in line with the slits and adjust its height so that it is horizontal and at the same height at the centre of slits and at a suitable distance from the slits. Focus the telescope on the slits and close slit of the telescope slowly till the image of the two slits of the card board superimpose upon each other and appear as just one.

Measure the minimum width of the travelling microscope. The difference of the two readings gives the width of the slit just sufficient to resolve the two images. Measure the distance between the telescope and the slit which gives D. Take reading for the width of the slit S with microscope in each case.

Record : vernier constant of microscope= wavelength of light used λ = No. Microscope reading for measurement of (d) Distance of glass plate from telescope (D) d/D Microscope reading for (a) λ/a First line Second line d One edge of slit Other edge of slit a

Result : since d/D= λ/a the relation is verified Precautions and Sources of Errors: The two slits should be very narrow , close to each other and also vertical. Adjustable slit should be perfectly vertical. Axis of the width of the slit with microscope should be done carefully and accurately. While using microscope for measuring the distance of the slit, backlash error should be avoided. Do not close the slit so tightly otherwise its edges get damaged.

Viva - Voce 1. What do you mean by resolving power of a telescope? 2. On what factors does the resolving power depend? 3. Define the magnifying power of the telescope. 4. What is Rayleigh criterion of resolution? 5. Why have the objectives of telescopes large apertures? 6. What is the resolving power of a normal eye? 7. What does the term 200 inch written on the telescope indicate? 8. What will be the resolving power of this telescope?