Which of the following conditions would decrease the ability of a person to hear a sound? a. the distance to the sound source becomes shorter. b. a wave loses energy as it moves through a medium. c. the liquid medium in which the sound travels is replaced with an elastic solid. d. the frequency of the sound remains steady at 100 hz.

wire in brush may conduct electricity from cell to drill and vice versa electrc shock possible

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