State parallelogram law of vector addition and derive an expression for the resutlant of two vectors `vecto P and vecto Q` inclined to each other at angle `theta`.

State triangle law of addition of vectors.

Two long straight thin conductors carrying currents I_1 and I_2 respectively along the same direction are placed parallel to each other in air. Derive an expression for the force per unit length acting on any one of the conductors and hence define one ampere current.

If vecu and vecv be two vectors parallel to each other then find vecu xx vecv .

State Coulomb's law of force in electrostatics. Express it in vector form.

If tangents PA and PB from a point P to a circle with centre O are inclined to each other at angle of 80^@ ,then anglePOA is equal to

State Coulomb's law of electrostatics. Express it in vector form.

.The sum and difference of two vectors are perpendicular to each other. Prove that the vectors are equal in magnitude.