The uncertainty principle can be used to estimate time and frequency scales governing optical transitions. make estimates for the following: (i) calculate the percentage uncertainty in the frequency ? ? /? of the emitted light when a hydrogen atom makes a transition from the fourth excited state to the ground state when the lifetime of the fourth excited state is ? -2.75 10.9 s. (ii) what is the lifetime of the ground state? give the reason for your answer. ii) a laser pulse has a linewidth defined as the uncertainty in the output (the spectral ine) wavelength ax. find an expression relating the linewidth of the laser's spectral line to the bandwidth which is the uncertainty in the frequency of the spectral line. (iv) if the duration of the laser pulse in ii) is 1.5 x 10-9 s, estimate the linewidth of the 632.8 nm beam from a hene laser.

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