Modern Physics - Physics Previous Year Questions

The decay constants of two radioactive substances X and Y are 4\(\lambda\) and \(\lambda\) respectively. At t = 0, a sample has the same number of two nuclei. The time taken for the ratio of number of nuclei to become \({1 \over {{e^3}}}\) will be

A proton has kinetic energy E = 100 eV which is equal to that of a photon. The wavelength of photon is \(\lambda\)₂ and that of proton is \(\lambda\)₁. The ratio \({{{\lambda _2}} \over {{\lambda _1}}}\) is proportional to

In the circuit shown assume the diode to be ideal. When V_i increases from \(-\)2V to 6V, the change in current is (in mA)

After two hours one-eight of the starting amount of a certain radioactive isotope remained undecayed. The half-life of the isotope is

Consider a hydrogen atom with its electron in the $n$th orbit. An electromagnetic radiation of wavelength 90 nm is used to ionize the atom. If the kinetic energy of the ejected electron is 10.4 eV , then the value of $n$ is ( $h c=1242 \mathrm{eV} \mathrm{nm}$ )