The wavelength of an X-ray beam is 10$$\mathop A\limits^o $$. The mass of a fictitious particle having the same energy as that of the X-ray photons is $${x \over 3}h$$ kg. The value of x is __________. (h = Planck's constant)

An electromagnetic wave of frequency 3 GHz enters a dielectric medium of relative electric permittivity 2.25 from vacuum. The wavelength of this wave in that medium will be _________ $$\times$$ 10^$$-$$2 cm.

An electromagnetic wave of frequency 5 GHz, is travelling in a medium whose relative electric permittivity and relative magnetic permeability both are 2. Its velocity in this medium is ____________ $$\times$$ 10⁷ m/s.

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)