If $\vec a$ is a non-zero vector of magnitude $'a'$ and $\lambda$ a non- zero scalar, then $\lambda \vec a$ is unit vector if

• $\lambda = 1$

• $\lambda = - 1$

• $a = |\lambda |$

• $a = 1/|\lambda |$

{Option d is Correct}

$\vec a$ is a non-zero vector of magnitude $a \Rightarrow |\vec a| = a$
Since $\lambda \vec a$ is a unit vector

$\Rightarrow |\lambda \vec a| = 1 \Rightarrow |\lambda ||\vec a| = 1 \Rightarrow |\lambda |a = 1$
$\Rightarrow a = \cfrac{1}{{|\lambda |}}$

Exercise-10.4