Replacing an arbitrary ‘black box’ ray matrix with a single lens. an optical black box has various optical elements inside it, producing a given real abcd matrix from its input plane to its output plane. we want to replace this black box with a box of physical length l, containing only a single lens of focal length f. can this be done? why? and if so, what total length l, focal length f, and lens location x (within l) will be required?

mistakes are ok

no sign of dia of fuel cell

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia