Charges Q₁ and Q₂ are at points A and B of a right angle triangle OAB (see figure). The resultant electric field at point O is perpendicular to the hypotenuse, then
$${{{Q_1}} \over {{Q_2}}}$$ is proportional to :

Suppose that intensity of a laser is $${{315} \over \pi }$$ W/m².
The rms electric field, in units of V/m associated with this source is close to the nearest integer is __________.

$$ \in $$₀ = 8.86 × 10^–12 C² Nm^–2; c = 3 × 10⁸ ms^–1)

A sound source S is moving along a straight track with speed v, and is emitting, sound of frequency v₀ (see figure). An observer is standing at a finite distance, at the point O, from the track. The time variation of frequency heard by the observer is best represented by:
(t₀ represents the instant when the distance between the source and observer is minimum)

The density of a solid metal sphere is determined by measuring its mass and its diameter. The maximum error in the density of the sphere is $$\left( {{x \over {100}}} \right)$$ %. If the relative errors in measuring the mass and the diameter are 6.0% and 1.5% respectively, the value of x is_______.