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State and explain the characteristics of vector product of two vectors.
Solution
$(1)$ $\vec{a} \times \vec{b}=\vec{b} \times \vec{a}$
The vector product of two vector is not commutative but $\vec{a} \times \vec{b}=-\vec{b} \times \vec{a}$ is opposite to each other
However $|\vec{a} \times \vec{b}|=|\vec{b} \times \vec{a}|$
$(2)$ Scalar product act behave like reflection (taking image in mirror) $x \rightarrow-x, y \rightarrow-y$ and $z \rightarrow$ $-z$.
In reflection occurrence all components changes sign mean positive vector becomes negative.
So, $\vec{a} \times \vec{b} \rightarrow(-\vec{a}) \times(-\vec{b})=\vec{a} \times \vec{b}$
Hence, in reflection sign is not change in resultant.
$(3)$ Vector product obeys distributive law :
$\vec{a} \times(\vec{b}+\vec{c})=\vec{a} \times \vec{b}+\vec{a} \times \vec{c}$
$(4)$ For two non-zero vectors $\vec{a} \times \vec{a}=\overrightarrow{0}$
where $\overrightarrow{0}$ is vector of zero modulus
Here $\vec{a} \times \vec{a} =(a)(a) \sin 0^{\circ} \hat{n}$ $=\overrightarrow{0}$
( $\because$ Angle between $\vec{a}$ and $\vec{a}$ is $0^{\circ}$ )
Hence, condition of parallel or anti parallel of two non-zero vectors is that its vector product should be zero.
$(5)$ If two non-zero vector is perpendicular, then
$\vec{a} \times \vec{b} =a b \sin 90^{\circ} \hat{n}$
$=a b \hat{n}$
where $\hat{n}$ is unit vector in direction of $\vec{a} \times \vec{b}$.
$(6)$ Vector product for unit vector of cartesian co-ordinate system.
Similar Questions
For component of a vector $A =(3 \hat{ i }+4 \hat{ j }-5 \hat{ k })$, match the following colum.
Colum $I$ | Colum $II$ |
$(A)$ $x-$axis | $(p)$ $5\,unit$ |
$(B)$ Along another vector $(2 \hat{ i }+\hat{ j }+2 \hat{ k })$ | $(q)$ $4\,unit$ |
$(C)$ Along $(6 \hat{ i }+8 \hat{ j }-10 \hat{ k })$ | $(r)$ $0$ |
$(D)$ Along another vector $(-3 \hat{ i }-4 \hat{ j }+5 \hat{ k })$ | $(s)$ None |