A 100W bulb together with its power supply is suspended from a sensitive balance. Find the change in the mass recorded after the bulb remains on for 1 year.
There is a physical significance of special theory of relativity that Energy and mass are interchangeable and that is given by Sir Einstein famous equation E=m
Loss in the mass due to continuous illumination of bulb
ATQ, the bulb illuminates for 1 year i.e 
with power of 1 W or 1 
Total energy dissipated by the bulb in the form of light energy will
be 
1