CBSE Class 12-science Answered
Plot graph for variation of 1 emf with external resistance 2 terminal potential difference with external resistance and 3 terminal potential difference with external resistance
Asked by rejimoljohn123 | 02 Jan, 2019, 09:30: PM
Expert Answer
EMF of battery is independent of external resistance.
When external resistance is changed in the circuit, EMF of battery remains constant.
This is shown in the graph drawn in the left side figure.
Let E is emf of battery, r is internal resistance and R is the exiernal resistance.
If i is the current flowing in the circuit due to the resitance R, then we have, E = i(r+R) .......(1)
Terminal voltage V = E- i × r ..............(2)
Using the equation.(2), eqn.(1) can be written as, V = i × R ..........(3)
By eliminating i using eqn.(1), eqn.(3) is written as V = 
.......................(4)
.......................(4)When external resistance R = 0, terminal voltage V = 0 .
This is due to maximum current flowing due to internal resistance only and all the potential drop is across internal resistance
When external resistance R >> internal resistance r, then magnitude of terminal voltage becomes EMF,
because current drawn is minimum and potential drop across internal resistance is negligible.
For example, if we take a 12 V battery with internal resistance 0.1Ω,
Then the variation of terminal voltage as given in eqn.(4) is plotted in the right side graph in figure.
Answered by Thiyagarajan K | 03 Jan, 2019, 12:01: AM
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