Upon examining layer m, you find that it contains a small proportion of the radioactive isotope - potassium-40, which decays into argon-40 with a half-life of 1.3 billion years. assuming no contamination, what would be the age of a this layer if it contained 25% of potassium-40 and 75% argon-40?

t = 2.6 billion years

Explanation:

If potassium becomes 25% of its initial value

so we can say it becomes half two times

as we know that 25% means it is 1/4 times of initial value

so we will have

here we know that

t = 2.6 billion years

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