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| 1. |
What is the length of the telescope when it forms the final image at infinity? |
| Answer» Solution :The objective LENS collects parallel rays from a DISTANT object. So, it forms the image at the FOCUS. `f_0` of the objective. As the final image is at infinity, the image formed by the objective must be at the focus `f_0` of the EYE PIECE. In other words when final image is formed at infinity, `f_0` and `f_e` coincide. Therefore, length of the tube of the telescope = `f_0+f_e` where `f-0` and `f_e` are focal lengths of objective and eye piece respectively. | |