Two identical cells each of emf 1.5 V are connected in parallel across a parallel combination of two resistors each of resistance 20 Ω. A voltmeter connected in the circuit measures 1.2 V. The internal resistance of each cell is

Question

Two identical cells each of emf 1.5 V are connected in parallel across a parallel combination of two resistors each of resistance 20 Ω. A voltmeter connected in the circuit measures 1.2 V. The internal resistance of each cell is (A) 2.5 Ω (B) 4 Ω (C) 5 Ω (D) 10 Ω

Tardigrade Admin · Accepted Answer

<img class="img-fluid question-image" alt="image" src="https://cdn.tardigrade.in/img/question/physics/804df2de3628ed39280150d2882d4e05-.png" /> V = E - ir / 2 1.2=1.5- i (( r /2)) i ( r /2)=0.3 i =(1.5/10+( r )2) ⇒ 10 i +( ir /2)=1.5 10 i =1.5-0.3 i =0.12 A ⇒ r =(0.6/0.12)=5 Ω

Q. Two identical cells each of emf $1.5 V$ are connected in parallel across a parallel combination of two resistors each of resistance $20 Ω$ . A voltmeter connected in the circuit measures $1.2 V$ . The internal resistance of each cell is

$2.5 Ω$

$4 Ω$

$5 Ω$

$10 Ω$

$V = E - i r /2$
$1.2 = 1.5 - i (\frac{r}{2})$
$i \frac{r}{2} = 0.3$
$i = \frac{1.5}{10 + \frac{r}{2}}$
$\Rightarrow 10 i + \frac{i r}{2} = 1.5$
$10 i = 1.5 - 0.3$
$i = 0.12 A$
$\Rightarrow r = \frac{0.6}{0.12} = 5 Ω$

Q. Two identical cells each of emf 1.5V are connected in parallel across a parallel combination of two resistors each of resistance 20Ω. A voltmeter connected in the circuit measures 1.2V. The internal resistance of each cell is

2.5Ω

4Ω

5Ω

10Ω