The unit used to measure electric current is the ampere (A). Now, assume that the current delivered at a wall socket reaches the value 3.8 A ten times in a time interval of 0.17 s. What is the period T with which the current at the wall socket changes?

T = 0.017s

Explanation:

period is the time it takes a particle to make one oscillation

An electric current is periodic in nature

The current reaches 3.8A  ten times.  

So there must have been 10 cycles (10 periods) in 0.17s.   let 'T'  be the period:

t is the total time interval

n is the number of oscillations

10T = 0.17

T = 0.17/10 = 0.017s

increase masses, decrease separation

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