current-electricity Question 37

Question: Q. 15. A cell of emf ’ 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 I.

It is found that when R=4Ω, the current is 1 A when R is increased to 9Ω, the current reduces to 0.5 A. Find the values of the emf E and internal resistance r.

A [Delhi I, II, III 2015]

Show Answer

Solution:

Ans. (i)

(ii)

1/2

I=ER+r I=E4+r

E=4+r

…(i) 1/2

From equation (i) and (ii),

2 4+r=4.5+0.5r1/2

Using this value of r, we get

E=5V

[CBSE Marking Scheme 2015]

Detailed Answer :

From (1) & (2)

the pots are:



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