With reference to the observations in photo-electric effect, identify the correct statements from below :

(A) The square of maximum velocity of photoelectrons varies linearly with frequency of incident light.

(B) The value of saturation current increases on moving the source of light away from the metal surface.

(C) The maximum kinetic energy of photo-electrons decreases on decreasing the power of LED (light emitting diode) source of light.

(D) The immediate emission of photo-electrons out of metal surface can not be explained by particle nature of light/electromagnetic waves.

(E) Existence of threshold wavelength can not be explained by wave nature of light/ electromagnetic waves.

Choose the correct answer from the options given below :

The activity of a radioactive material is $$6.4 \times 10^{-4}$$ curie. Its half life is 5 days. The activity will become $$5 \times 10^{-6}$$ curie after :

For a constant collector-emitter voltage of $$8 \mathrm{~V}$$, the collector current of a transistor reached to the value of $$6 \mathrm{~mA}$$ from $$4 \mathrm{~mA}$$, whereas base current changed from $$20 \,\mu \mathrm{A}$$ to $$25 \,\mu \mathrm{A}$$ value. If transistor is in active state, small signal current gain (current amplification factor) will be :

A square wave of the modulating signal is shown in the figure. The carrier wave is given by $$C(t)=5 \sin (8 \pi t)$$ Volt. The modulation index is :