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Ohm''s Law - Engineering

Q1:

A 120 V lamp-dimming circuit is controlled by a rheostat and protected from excessive current by a 3 A fuse. To what minimum resistance value can the rheostat be set without blowing the fuse? Assume a lamp resistance of 20 ohms.

A 40 

B 4 

C 2 

D 20 

ANS:D - 20 

As resistance is inversely proportional to current. So to calculate minimum resistance we have to consider max. Current through the circuit. So, I=3 A and with the help of this we can find answer as per the mentioned solutions.