The clock stop when switching focus I have notice that when I switch my focus from existing task to a clock (both digital, which shows numbers, and mechanical, which shows arms), the time on the clock seem to stop ticking for a brief moment.

So, my question is that does this phenomena has a term? Is there any explanation why this will happen? Is this common or is this a problem only few person would ever experience?

Since I am new to this field, I would also like to know how to tag this kind of question. Thank you very much.
Yes, there is a term for this phenomenon. It is called stopped-clock illusion. It’s a type of chronostasis or a kind of temporal illusion, that the time interval is perceived to be longer than it really is.

Though I’m not totally convinced myself, the current explanation is like this:

This phenomenon happens because the brain fills in the perception gap that occurs (while changing visual targets) with the end visual target. This is because, when we change visual targets by moving our eyes, the overall visual scene will become blurred during that time and the brain avoids this confusing visual input by suppressing it, which results in a perception gap during that period of time. When the gaze changing ends, the brain fills this gap with the static image of the end visual target instead. As a result, the end visual target will be perceived to exist longer than it is actually seen. This suppressing of the blurred image also explains why we never experience blurry images while we move our eyes to see things around us.

References:


Wikipedia. Chronostasis
BBC Future. The mystery of the stopped clock illusion


More in-depth, academic references:


Eagleman DM. Human time perception and its illusions. Curr Opin Neurobiol. 2008 April;18(2):131–136.
van Wassenhove V, Wittmann M, Craig AD, Paulus MP. Psychological and neural mechanisms of subjective time dilation. Front Neurosci.2011;5:56.