Question
Sat February 11, 2012

In figure AB is a potentiometer wire of length 10 m and resistance . With key K open, the balancing length is 5.5 m. However on closing key K the balancing length reduces to 5 m. The internal resistance of the cell is. answer is 0.1ohm but i think wouldn't the current be zero in both cases through the cell

Mon February 13, 2012
Internal resistance, r= [(l1 -l2)/l2]R
r= [(5.5-5.0)/5]x1
r= 0.5/5 =0.1 ohm
when the balanced point is obtained on the potentiometer wire, no current flows in the galvanometer circuit because the fall of potential across the potentiometer wire between zero end and balance point position becomes just equal to the e.m.f of the cell, whereas the current in the potentiometer wire continues flowing.
Related Questions
Wed January 18, 2017

# A cell of emf E and internal resistance r is connected to two external resistance R1 and R2 and a perfect ammeter.The current in the circuit is measured in four different situation: (i)without any external resistance in the circuit (ii)with resistance R1 only (iii)with Ri and R2 in series combination (iv)with R1 and R2 in parallel combination The currents measured in the four cases are 0.42A,1.05A,1.4A and 4.2A,but not necessarily in that order.Identify the currents corresponding to the four cases mentioned above.

Thu November 24, 2016

Home Work Help