A potentiometer wire AB having length L and resistance 12 r is joined to a cell D of emf ε and internal resistance r. A cell C having emf ε/2 and internal resistance 3r is connected. The length AJ at which the galvanometer as shown in figure. shows no deflection is:
Text Solution
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Given, length of wire, 
Resistance of wire, 
emf of cell 
, internal resistance of 
emf of cell 
, internal resistance of 
Current in potentiometer wire 
Potential drop across the balance length 
of potentiometer wire is
where, 
is the balance length 
.
As null point occurs at 
, so potential drop across balance length,
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