A compound microscope consists of an objective lens of focal length 1 cm and an eye piece of focal length 5 cm with a separation of 10 cm . The distance between an object and the objective lens,at which the strain on the eye is minimum is  n40. The value of n is ____

Strain is minimum this implies final image is at far point and intermediate image is at focal length of eye piece . That means intermediate image distance from objective is (10-5=5cm).Lens formula for objective lens, ​1f=1v−1u​⇒1+1=1+5−1u​⇒u=−54​Object distance=5040cm