Why does light of a certain frequency need to be used to produce a current in the photoelectric effect? a. the frequency of light must be the same as the frequency of vibration of the atoms in the substance to cause a current. b. the atoms can only lose their electrons when they are provided with packages of energy of a certain discrete amount. c. the atoms of the substance require specific frequencies of light to cause them to vibrate. d. only light of certain frequencies can penetrate the substance to a sufficient depth to cause the atoms to react.

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