Explanation

(d) The time period of a simple pendulum is
$T = 2\pi\sqrt{\frac{l}{g}}$
[image:14_image80.emf]
Here, $l$ is the length of the pendulum.
On squaring both sides
$T^{2} = \frac{4\pi^{2}l}{g}$
$\Rightarrow$ $T^{2} \propto l$
So, the graph between time period $T$ and length $l$ of the pendulum is a parabola.