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Ultra Thin Films

Films having thickness below 100 Ao.

Ultrasonic Waves

Sound waves of high frequency greater than 20,000 Hz are called as ultrasonic waves. These frequencies are beyond audible limit.


(Latin for “shadow”) is the innermost and darkest part of a shadow, where the light source is completely blocked by the occluding body.

Uniaxial Crystal

It is a double refracting crystal which has only one axis along which both the refracted rays have same speed. Ex: Calcite, Quartz, etc.

Uniform Circular Motion

 The motion of an object with constant speed in a circle.

Unit Cell

Basic structural unit or building block of crystal structure, which   defines the crystal structure by virtue of its geometry and the atom positions within it. A unit cell is chosen to represent the symmetry of crystal structure, where in all the atom positions in the crystal may be generated by translation of unit cell integral distances along each of its edges.  

Universal Gravitational Constant

 It is the force between two unit masses separated by unit distance is called universal gravitational constant. The value of ‘G’ is 6.67 x 10-11 Nm2Kg-2

Unsaturated Vapor

 If a liquid is in open container, the vapor molecules rapidly diffuse away from liquid, and in general produce unsaturated vapor.