A ‘thermal tap’ used in a certain apparatus consists of a silica rod which fits tightly inside an aluminium tube whose internal diameter is 8mm at

0

0C. When the temperature is raised, the fit is no longer exact. Calculate

what change in temperature is necessary to produce a channel whose

cross-section is equal to that of a tube of 1mm internal diameter. (linear

expansivity of silica = 8X10-6

/K and linear expansivity of aluminium =

26X10-6

/K )

that would be because of both gravity and friction. so     c

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