Sarah and maria made a telephone using two cans and a string. it was a very long string. maria went upstairs in her house and sarah stayed downstairs. maria spoke softly into the can. "i can hear you! ' sarah said back. how can this happen? a)sound waves travel through a vacuum. b)sound waves travel from high to low. c)sound waves travel through solids like the string. eliminated)maria talked so loudly that sarah could hear her without the phone.

show the wavelengths of a wave. show the crests of a wave.

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