Focal length of the Objective lens is 140 cm. Focal length of the eyepiece is 5cm. If this telescope is used to view a 100 m tall tower 3 km away, what is the height of the image of the tower formed by the objective lens ?

Explanation

Angle subtended by the tower = `alpha`
`alpha = ("height of the power " )/(" Distance between the telescope and tower ") = (100)/(3000) = (1)/(30) `
Let.h. be height of the image. Then
`alpha = (h)/(f_(0)) = (h)/(140 ) " " therefore (h)/(140) = (1)/(30) " " h =(140)/(30) = 4.7 ` cm