Which one of the following statements is correct?

When radiation of the wavelength $\lambda$ is incident on a metallic surface,the stopping potential is $4.8 \ V$. If the same surface is illuminated with radiation of double the wavelength,then the stopping potential becomes $1.6 \ V$. Then,the threshold wavelength for the surface is:

In the circuit shown in the figure,the current $I$ is: (in $\,A$)

$\int \frac{1+x+\sqrt{x+x^2}}{\sqrt{x}+\sqrt{1+x}} d x$ is equal to

Pulses are obtained from which family?

At room temperature,a $P-$ type semiconductor has