Current Electricity and Electrical InstrumentHard
Question
An electric bell has a resistance of 5Ω and requires a current of 0.25 A to work it. Assuming that the resistance of then bell wire is 1Ω per 15m and that the bell push is 90m distance from the the bell. How many cells each of emf 1.4V and internal resistance 2Ω, will be required to work the circuit -
Options
A.3
B.4
C.5
D.Can′t be determined
Solution
Total length of wire = 90 + 90 = 180 m ;
Total number of wire = 180/5 = 12Ω.
As I =
⇒ 0.25 = 
⇒ n = 4.7
⇒ Total number of cells required = 5
Total number of wire = 180/5 = 12Ω.
As I =
⇒ 0.25 = ⇒ n = 4.7⇒ Total number of cells required = 5
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