Physics M.C.Q (1 Marks)

It's been determined experimentally that when light shines on a metal surface, the surface emits electrons. For example, you can start a current in a circuit just by shining a light on a metal plate. we were saying earlier that light is made up of electromagnetic waves, and that the waves carry energy. So if a wave of light hit an electron in one of the atoms in the metal, it might transfer enough energy to knock the electron out of its atom. Light has sometimes been viewed as a particle $($photon$)$ rather than a wave. If it's waves, the energy contained in one of those waves should depend only on its amplitude$--$that is, on the intensity of the light.

First electron shell which is closest to the orbit to the nucleus, called the $1s$ orbit can hold up two two electrons. This orbit is equivalent to the innermost electron shell of the Bhor model of atom. It is called the orbital because it is spherical around the nucleus.

Line respectrum is characteristic of the element because it obtained of atoms only. Continous spectrum is characteristics of the source of light.
In the spectrum of sodium, there are two prominent yellow lines of wavelength $589.0\ nm$ and $589.6\ nm.$
Absorption line spectrum is not characteristic of the element.

According to Bohr's atomic theory, the orbital angular momentum of an electron is an integral multiplt of $\frac{\text{h}}{2\pi}$
$\therefore\ \text{L}_\text{n}=\frac{\text{nh}}{2\pi}$
Here,
$n =$ Principal quantum number
The minimum of $n$ is $1$
Thus, the minimum value of the orbit angular momentum of the electron in a hydrogen is given by $\text{L}=\frac{\text{h}}{2\pi}$

Key concept: Total energy $(E)$ is the sum of potential energy and kinetic energy, i.e.$ E = K + U$
$\Rightarrow\ \text{E}=-\frac{\text{kZe}^2}{2\text{r}_\text{n}}\text{also r}_\text{n}=\frac{\text{n}^2\text{h}^2\in_0}{\pi\text{mze}^2}$
Hence $\text{E}=-\bigg(\frac{\text{me}^4}{8\in_0^2\text{h}^2}\bigg)\frac{\text{Z}^2}{\text{n}^2}=-\bigg(\frac{\text{me}^4}{8\in_0^2\text{ch}^3}\bigg)\text{ch}\frac{\text{Z}^2}{\text{n}^2}$
$=-\text{R ch}\frac{\text{Z}^2}{\text{n}^2}=-13.6\frac{\text{Z}^2}{\text{n}^2}\text{eV}$
The lowest state of the atom, called the ground state, is that of the lowest energy. The energy of this state $(n = 1), E_1$ is $-13.6\ eV$
Energy level diagram of hydrogen/hydrogen like atom:

Transition from higher states to $n = 2$ lead to emission of radiation with wavelengths $656.3\ nm$ and $365.0\ nm.$
These wavelengths fall in the visible region and constitute the Balmer series.

The wavelength corresponding the transition from $n_2$ to $n_1$ is given by,
$\frac{1}{\lambda}=\text{RZ}^2\Big(\frac{1}{\text{n}^2_1}-\frac{1}{\text{n}^2_2}\Big)$
Here,
$R =$ Rydberg constant.
$Z =$ Atomic number of the ion.
From the given formula, it can be observed that the wavelength is inversely proportional to the square of the atomic number.
Therefore, the wavelength corresponding to $n = 2$ to $n = 1$ will be minimum in doubly ionized lithium ion because for lithium, $Z = 3.$

All the photons emitted in the laser move with the speed equal to the speed of light $(c = 3 \times 10^8m/s)$. Ideally, the light wave through the laser must be coherent, but in practical laser tubes, there is some deviation from the ideal result. Thus, the photons emitted by the laser have little variations in their wavelengths and energies as well as the directions, but the velocity of all the photons remains same.

The hydrogen atom is stable when the electron rests at the ground level of energy, i.e. when the principal quantum number, $n = 1. '$
In other words, when the electron is revolving in the first orbit around the nucleus, the hydrogen atom is stable.

Neil Bohr proposed the concept of stationary orbits in $1913$, which is now called the Bohr model of atom. The electron can only orbit stably, without radiating, in certain orbits at a certain discretesct of distance from the nucleus.

A discharge tube is a tube containing charged electrodes and filled with a gas in which ionization is induced by an electric filed. $X-$ray tube, fluroscent tube and cathode rays oscilloscope can be used as a modified discharge tube in which these tubes contain charged electrodes and filled with a gas.

The proton, neutron, and electron possess half$-$integer spin states

Coulomb force is responsible for scattering of particles. When the alpha particles $($positive in charge$)$ get closer to the nucleus, which is positive in charge, they get repelled through various angles.