Physics
Holography is a technique of

Recording a permanent, sharp two diimensional black and white or multicolour photograph
Recording a permanent three dimensional black and white photograph
Recording a permanent three dimensional photograph of a given single colour or a multicolour
Recording a permanent three dimensional multicolour photograph

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Physics
Why two thin shirts can keep us warmer than a single thick shirt in winter ?

Air layer between two shirts behaves like insulating media
No radiation of heat takes place
Two thin shirts become thicker so prevent transmission of heat
Air layer between two shirts works as good conductor

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