What is the $SI$ unit of luminous intensity?

Can the resultant of three vectors of unequal magnitudes be a zero vector?

What is a position vector? What is a displacement vector? Explain the equality of vectors.

$A$ vector makes $45^{\circ}$ and $60^{\circ}$ angles with the $x$ and $y$ axes respectively. The unit vector along the given vector is:

Calculate the de Broglie wavelength of an electron in the first Bohr orbit of a hydrogen atom if the velocity of an electron in the first orbit is $2.2 \times 10^6 \text{ m s}^{-1}$. [mass of electron = $9.1 \times 10^{-31} \text{ kg}$, Planck's constant $(h)$ = $6.626 \times 10^{-34} \text{ J s}$]

If a vector $\overrightarrow{P}$ makes angles $\alpha, \beta,$ and $\gamma$ with the $X, Y,$ and $Z$ axes respectively,then $\sin^2 \alpha + \sin^2 \beta + \sin^2 \gamma = $