1.A light bulb emitting 1750 lm of luminous flux shines on a book that is 3.0 m away. a. What is the illumination on the book?
b. In general terms, how will illuminance change as a person in the room moves the book closer to the light bulb? How does this illustrate an inverse-square relationship?

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.

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