Question

The current flowing through a resistor connected in an electric circuit and the potential difference applied across its ends are shown in the figures below:



The value of the resistance of the resistor is :
(1) 10 Ω
(2) 15 Ω
(3) 20 Ω
(4) 25 Ω

Answer 1

Least count of milliammeter scale =$\frac{300\text{mA}}{15}=20\text{mA}$

Value of current = 9$\times$20 mA = 180 mA

Least count on voltmeter scale = $\frac{3}{15}=0.2\text{V}$

Value of voltage applied = 9$\times$0.2 V = 1.8 V

According to Ohm's law,

$$\begin{gathered} V=IR\mathrm{o}\text{r}R=\frac{V}{I} \\ \Rightarrow R=\frac{1.8\text{V}}{180\times {10}^{-3}\text{A}}=10\text{Ω} \\ \Rightarrow R=10\text{Ω} \end{gathered}$$

Hence the correct answer is Option 1.