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  • 17 A cell of emf (E) and internal resistance (r) is connected across a variable external resistance (R). Plot graphs to show variation of  (i) E with R,  (ii) Term

A cell of emf (E) and internal resistance (r) is connected across a variable external resistance (R). Plot graphs to show variation of

 (i) E with R

 (ii) Terminal p.d. of the cell (V) with

 

Answers (1)

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(i) Variation of emf E with external resistance RRR

  • The emf of a cell is a constant property of the cell.

  • It does not depend on the external resistance RRR.

Graph:

  • Plot E on the y-axis and RRR on the x-axis.

  • Since E is constant, the graph is a straight horizontal line, parallel to the x-axis.

Conclusion:

E=constant (independent of R)E = \text{constant (independent of } R\text{)}E=constant (independent of R)

(ii) Variation of terminal potential difference VVV with external resistance RRR

The terminal potential difference of a cell is given by:

V=E−Ir

But current,

I=E/(R+r)?

Substituting:

V=E−{Er/(R+r)}?

Observations:

  • When R=0R = 0R=0 (short circuit):

    V=0

  • When R→∞

    I→0⇒V→E

So, as R increases:

  • Current decreases

  • Drop across internal resistance decreases

  • Terminal voltage increases, approaching E

Graph:

  • Plot VVV on the y-axis and RRR on the x-axis.

  • The curve starts from the origin and rises gradually, approaching the horizontal line V=EV = EV=E.

  • The graph is a non-linear curve.

 

 

Posted by

Saumya Singh

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