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Q. No.An astronomical telescope has objective and ocular focal lengths of 100 cm and 1 cm respectively. The minimum magnifying power of the telescope is:
1. 50
2. 100
3. 96
4. 48
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A giant refracting telescope at an observatory has an objective lens of focal length \(15\) m. If an eyepiece of focal length \(1.0\) cm is used, what is the angular magnification of the telescope?
| 1. | \(1175\) | 2. | \(1250\) |
| 3. | \(1300\) | 4. | \(1500\) |
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The magnifying power of a telescope is \(9\). When it is adjusted for parallel rays the distance between the objective and eyepiece is \(20~\text{cm}\). The focal length of the lenses is:
| 1. | \(10~\text{cm}, ~10~\text{cm}\) | 2. | \(15~\text{cm}, ~5~\text{cm}\) |
| 3. | \(18~\text{cm}, ~2~\text{cm}\) | 4. | \(11~\text{cm}, ~9~\text{cm}\) |
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AIPMT - 2012
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An astronomical telescope has an angular magnification of magnitude \(5\) for distant objects. The separation between the objective and the eyepiece is \(36~\text{cm}\) and the final image is formed at infinity. The focal length \(f_o\) of the objective and the focal length \(f_e\) of the eyepiece are:
| 1. | \(f_o=45~\text{cm}~\text{and}~f_e=-9 ~\text{cm}\) |
| 2. | \(f_o=7.2~\text{cm}~\text{and}~f_e=5 ~\text{cm}\) |
| 3. | \(f_o=50~\text{cm}~\text{and}~f_e=10 ~\text{cm}\) |
| 4. | \(f_o=30~\text{cm}~\text{and}~f_e=6 ~\text{cm}\) |
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To increase magnifying power of a telescope:
| 1. | focal length of eyepiece should be increased. |
| 2. | focal length of objective should be increased. |
| 3. | wavelength of light should be increased. |
| 4. | aperture of eyepiece should be increased. |
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A lens of large focal length and large aperture is best suited as an objective of an astronomical telescope since:
| 1. | a large aperture contributes to the quality and visibility of the images. |
| 2. | a large area of the objective ensures better light-gathering power. |
| 3. | a large aperture provides a better resolution. |
| 4. | all of the above. |
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NEET - 2021
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A distant object, when viewed under normal adjustment, using an astronomical telescope forms an image that is magnified by \(50.\) The eyepiece has a focal length of \(2~\text{cm}.\) The focal length of the objective is:
| 1. | \(100~\text{cm}\) | 2. | \(25~\text{cm}\) |
| 3. | \(5000~\text{cm}\) | 4. | \({\large\frac{2}{50}}~\text{cm}\) |
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A refracting telescope consists of an objective lens \((O, \text{focal length }f_O)\) and an eyepiece \((E,\text{focal length }f_E)\) placed co-axially, with a separation \(d.\) The object is at infinity and the image formed by the objective lens is viewed through the eyepiece: the eye being placed just behind the eyepiece, \(E.\)
If the final image, seen by the eye, is at infinity, the separation \(d\) is given by:
If the final image, seen by the eye, is at infinity, the separation \(d\) is given by:
| 1. | \(d=f_O-f_E\) | 2. | \(d=f_O+f_E\) |
| 3. | \(d=f_O\) | 4. | \(d=\)\(\large\frac{f_O+f_E}{2}\) |
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The magnifying power of an astronomical telescope is \(8,\) and the distance between the two lenses is \(54\) cm. The focal lengths of the eye lens and the objective lens are, respectively:
| 1. | \(6\) cm and \(48\) cm |
| 2. | \(48\) cm and \(6\) cm |
| 3. | \(8\) cm and \(64\) cm |
| 4. | \(64\) cm and \(8\) cm |
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