In an experiment, DNA is treated with the compound which tends to place itself amongst the stacks of nitrogenous base pairs. As a result of this, the distance between two consecutive base increases. From 0.34 - 0.44 nm calculate the length of DNA double helix (which has `2xx10^9` bp) in the presence of saturating of this compound.

A person with a normal near point (25 cm) using a compound microscope with objective of focal length 8.0 mm and an eyepiece of focal length 2.5cm can bring an object placed at 9.0mm from the objective in sharp focus. What is the separation between the two lenses? Calculate the magnifying power of the microscope.

In figure S is a monochromatic point source emitting light of wavelength lambda=500 nm. A thin lens of circular shape and focal length 0.10 m is cut into two identical halves L_(1) and L_(2) by a plane passing through a doameter. The two halves are placed symmetrically about the central axis SO with a gap of 0.5 mm. The distance along the axis from A to L_(1) and L_(2) is 0.15 m , while that from L_(1) and L_(2) to O is 1.30 m. The screen at O is normal to SO. (b) If the gap between L_(1) and L_(2) is reduced from its original value of 0.5 mm, will the distance OP increases, devreases or remain the same?