When a resistance of 6ohms is connected across the terminals of a cell, the terminal potential difference is found to be 4.5V. When another resistance of 6 ohms is connected across the cell , the terminal potential difference becomes 3.6V.What will be the potential difference between the terminals of the cell when one more resistance of 6ohms is connected across the combination ?

Question

radar · Answer

The steps you need to solve this are as follows:
1.  You must calculate the internal resistance of the battery.  Note the drawing:|dw:1410875424818:dw|
Step 2.  Determine the change in current for the change in voltage.  You are given the change in voltage.  It changed from 4.5 volts to 3.6 volt (just a matter of subtraction.
To calculate the change in current:  Figure the current for the upper ckt.  This is where the voltage is 4.5 volts when resistance is 6 Ohm's.  Use Ohms Law.
Now calculate the current in the lower circuit.  Use Ohms Law, Voltage is given as 3.6 volts, Resistance is the effective resistance of two 6 Ohm resistors in parallel.  Compute that.  What do you get for the current in the lower circuit?
Compute the change in current.......

Now calculate the value of the internal resistance and the battery rated voltage.

R = change in voltage divided by change in current.  I will stop here to see what you come up with>