Question

how do the historians decide that A particular period has ended and other
period began
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Answer 1

Answer:

Find the position and nature of the image of an object 3 cm high placed at a distance 6 cm from a concave mirror of focal length 12 cm.

Answer 2

Periodization is the process or study of categorizing the past into discrete, quantified named blocks of time. ... However, determining the precise beginning and ending to any 'period' is often arbitrary, since it has changed over time over the course of history.