Asmall mass m hangs at rest from a vertical rope of length ℓ that is xed to the ceiling. a force then pushes on the
mass, perpendicular to the taut rope at all times, until the rope is oriented at an angle θ = θ0 and the mass has been
raised by a vertical distance h. assume the force’s magnitude f is adjusted so that the mass moves at constant
speed along its curved trajectory. show that the work done by during this process equals mgh, which is equivalent to the amount of work it takes to slowly lift a mass m straight up by a height h. [hint: when the angle is increased by dθ (in radians), the mass moves along an arc length ds = ℓ dθ.]

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