Choose the correct statement. In conductors

For a transistor, the current ratio $$\alpha_{\mathrm{dc}}=\frac{69}{70}$$, the current gain $$\beta_{\mathrm{dc}}$$ is

The input a.c. voltage of frequency $$60 \mathrm{~Hz}$$ is applied to half-wave rectifier and also to full-wave rectifier. The output frequency in case of half-wave rectifier and that in case of full wave rectifier is respectively.

A p-n junction photodiode is fabricated from a semiconductor with a band gap of $$2.5 \mathrm{~eV}$$. It can detect a signal of wavelength [Planck's constant $$=6.6 \times 10^{-34} \mathrm{Js}, \mathrm{c}=3 \times 10^8 \mathrm{~m} / \mathrm{s}, \mathrm{e}=1.6 \times 10^{-19} \mathrm{C}$$]