NEET UG 2021 — Modern Physics

The photoelectric effect was explained by

Consider the following statements (A) and (B) and identify the correct answer. (A) A Zener diode is connected in reverse bias when used as a voltage regulator. (B) The potential barrier of $p-n$ junction lies between $0.1V$ to $0.3V$.

A radioactive nucleus $\begin{matrix}A \\ Z\end{matrix}X$ undergoes spontaneous decay in the sequence $\begin{matrix}A \\ Z\end{matrix}X\rightarrow \begin{matrix} \\ (Z-1)\end{matrix}B\rightarrow \begin{matrix} \\ (Z-3)\end{matrix}C\rightarrow \begin{matrix} \\ (Z-2)\end{matrix}D$, where $Z$ is the atomic number of element $X$. The possible decay particles in the sequence are:

An electromagnetic wave of wavelength $\lambda$ is incident on a photosensitive surface of negligible work function. If $m$ mass is of photoelectron emitted from the surface has de-Broglie wavelength ${\lambda }_{d}$, then :

A nucleus with mass number $240$ breaks into two fragments each of mass number $120,$ the binding energy per nucleon of unfragmented nuclei is $7.6\mathrm{MeV}$ while that of fragments is $8.5\mathrm{MeV}$. The total gain in the binding energy in the process is :

For the given circuit, the input digital signals are applied at the terminals $A,B$ and $C$. What would be the output at the terminal $y$ ?  

The electron concentration in an undefined $n$-type semiconductor is the same as hole concentration in a undefined $p$-type semiconductor. An external field (electric) is applied across each of them. Compare the currents in them.

The number of photons per second on an average emitted by the source of monochromatic light of wavelength $600\mathrm{nm}$, when it delivers the power of $3.3\times {10}^{-3}W$ will be $:(h=6.6\times {10}^{-34}Js)$

The half-life of a radioactive nuclide is $100$ hours. The fraction of original activity that will remain after $150$ hours would be :