A Galilean telescope measures 27 cm in length when it is focussed to produce an image at infinity. Determine the focal length of the eyepiece, given that the objective has a focal length of 30 cm .

Step-by-step solution

For a Galilean telescope in normal adjustment (image at infinity), the length of the telescope tube is given by the difference between the focal length of the objective and the magnitude of the focal length of the eyepiece. L = f_o - f_e Given that the length of the telescope L = 27 cm and the focal length of the objective f_o = 30 cm . Substituting the given values: 27 = 30 - f_e f_e = 30 - 27 = 3 cm The focal length of the eyepiece is 3 cm .