The efficiency of a cell when connected to a resistance R is 60 %. What will be its efficiency if the external resistance is increased to six times.

Question

The efficiency of a cell when connected to a resistance R is 60 %. What will be its efficiency if the external resistance is increased to six times. (A) 90 % (B) 60 % (C) 80 % (D) 10 %

Tardigrade Admin · Accepted Answer

For Ist case efficiency = (TPD/EMF)× 100=(E R / R + r/E)=(R/R + r) 0.6=(R/R + r) Hence r=(2/3)R In 2nd case x=(6 R/6 R + r) Put the value of r and get the answer.

Q. The efficiency of a cell when connected to a resistance $R$ is $60%.$ What will be its efficiency if the external resistance is increased to six times.

$90%$

$60%$

$80%$

$10%$

For $I^{s t}$ case
efficiency $=$
$\frac{TP D}{EMF} \times 100 = \frac{ER / R + r}{E} = \frac{R}{R + r}$
$0.6 = \frac{R}{R + r}$
Hence $r = \frac{2}{3} R$
In $2^{n d}$ case
$x = \frac{6 R}{6 R + r}$
Put the value of $r$ and get the answer.

Q. The efficiency of a cell when connected to a resistance R is 60%. What will be its efficiency if the external resistance is increased to six times.

90%

60%

80%

10%