Question
Thu August 02, 2012 By: Swarnalakshmi Murugan

A bulb is rated 120V.But it is to be connected to a mains supply of 80V.How does the current flow and brightness change?

Expert Reply
Fri August 03, 2012
In the given case,
rated voltage, V1= 120V
applied Voltage, V2= 80V
 
Let current in the rated case be: I1
and in second case: I2
 
Since resistance of the bulb be R.
 
I1 = 120/R
 
I2 = 80/R
 
thus I1/I2 = 3/2
 
and since power is dirctly proportional to I2
Thus,
P1/P2 = 9/4
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