A potential difference of 12 V is applied across a resistor and a current of 3 A flows. What is its resistance?

1. By Ohm's law, $R = \dfrac{V}{I}$. 2. Substitute $V = 12\,\text{V}$ and $I = 3\,\text{A}$. 3. $R = \dfrac{12}{3} = 4\,\Omega$. 4. Choosing 36 mistakenly multiplies $V\times I$ (that gives power, not resistance). _Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 4 Electricity "Electricity", p.62_