A cell of E.M.F 'E' and internal resistance 'r' is connected across a variable load resistor R. Draw the plots of the terminal voltage V versus
(i) R and
(ii) the current .
It is found that when R=4Ω, the current is 1A when R is increased to 9Ω, the current reduces to 0.5 A. Find the values of the E.M.F E and internal resistance r.
Step 1: Given
A cell of emf 'E' and internal resistance 'r' and a variable load resistor R.
when then current i is and
when then current i is .
Step 2: Draw the graph
(i) Graph between the terminal voltage V and variable load resistor R-
(ii) Graph between the terminal voltage V and current i-
Step 3: find the emf E and internal resistance r
In condition 1, and
Terminal voltage, and
so,
put the value of R and i-
then, …(1)
In condition 2, and
and
now, put the value of R and
then, …(2)
Subtract equation 2 from equation 1-
now put value of r in equation 1,
Thus, the emf is 5V and internal resistance is .
Hence, the values of the emf E and internal resistance r is and respectively.