Question

A voltmeter is connected in parallel with a variable resistance $R$ which is in series with an ammeter and a cell as shown in figure. For one value of $R$, the meters read $0.3A$ and $0.9V$. For another value of $R$ the readings are $0.25A$ and $1.0V$. What is the internal resistance of the cell

• A. $0.5\Omega$
• B. $2\Omega$
• C. $1.2\Omega$
• D. $1\Omega$

Answer 1

The correct option is B $2\Omega$

In first case

$I=0.3A$

$V=0.9v$

It is known that

$V=E-Ir$

$⟹0.9=E-0.3r\to \left(1\right)$

In second case

$0.1=0.05r$

or $r=2\Omega$