How many 176 Ω resistors (in parallel) are required to carry 5A on a 220V line?
Step 1 : Equivalent resistance
Let n be the number of resistors to be connected in parallel
Then, R1=R2=......=Rn=R=176 Ω
Now, 1Req=1R1+1R2+.....1Rn
⇒1Req=nR1=n176
⇒Req=176/n ....(1)
Step 2 : Applying Ohm's law
V=IReq
⇒220=5Req
⇒220=5×176/n (Using Equation (1))
⇒n=4
Hence, four resistors are required.