A resistor develops 800 J of thermal energy in 20 s on applying a potential difference of 20 V. Its resistance is

10 Ω

The correct answer is Option (2) → 10 Ω

$\text{Given: } V = 20\,\text{V}, \, t = 20\,\text{s}, \, H = 800\,\text{J}$

$\text{Using Joule’s law: } H = \frac{V^2}{R} \, t$

$\Rightarrow R = \frac{V^2 t}{H}$

$R = \frac{20^2 \times 20}{800}$

$R = \frac{400 \times 20}{800} = 10\,\Omega$

$\text{Answer: } R = 10\,\Omega$