Light can travel long distances through optical fibers due to the phenomenon of total internal reflection. But if anything touches the surface of the fiber, it messes up the reflection and causes light to leave the fiber. To prevent this, the core of the optical fiber is typically surrounded by a cladding made of a lower index of refraction material. This keeps things away from the surface of the core. But because the cladding has an index higher than that of air, the critical angle is larger than it would have been than if the core were in contact with the air. Required:
If the core of an optical fiber has an index of refraction of 1.624 and the cladding has an index of refraction of 1.311, what is the critical angle for total internal reflection?

the electric field is a “force field” around a charged object that illustrates the direction the electric force would push an imaginary 

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