voltage cannot be assumed as fixed.u need to measure voltage too.and its not high voltage if talking interms of voltage and power.high voltage comes of 1000s of volts.so dont get yourself demotivated by using such words.
Power P = Voltage X Current X cos(fi) where cos(fi)is the power factor.in most domestic applications the power factor wil be almost 1.
so u need to just rig up a ckt to measure voltage n current.since its a college project u can do it easily without worrying about the accuracy,reliability and with of state-of-art technology.
do you?
Cheers!