Working Principle of a periscope is Reflection ( from the plane mirrors)
Working Principle of a magnetic compass is its magnetic properties especially it directionality.
Working Principle of Water cloack is Working Principle of Water clock is “time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel where the amount is then measured”.
We have a few videos on "Electricity And Circuits" of Class VI Science. Watch it for your reference - to find an answer to this question.