Can you explain this a bit more I don’t quite understand
No it's the quite opposite simple
Electromagnets can be turned off, this makes it easier to release things from the magnetic field.
Hope this helps :)
To solve this problem we will apply the concept of magnification, which is given as the relationship between the focal length of the eyepieces and the focal length of the objective. This relationship can be expressed mathematically as,

Here,
= Magnification
= Focal length eyepieces
= Focal length of the Objective
Rearranging to find the focal length of the objective

Replacing with our values


Therefore the focal length of th eobjective lenses is 27.75cm