Modern Physics PYQ — Page 8

An electron of hydrogen atom on an excited state is having energy ${E}_{n}=-0.85\mathrm{eV}$. The maximum number of allowed transitions to lower energy level is _______.

The acceptor level of a p-type semiconductor is $6 \mathrm{eV}$. The maximum wavelength of light which can create a hole would be : Given $\mathrm{hc}=1242 \mathrm{eV} \mathrm{nm}$.

The threshold frequency of a metal with work function $6.63\mathrm{eV}$ is :

In the given circuit if the power rating of Zener diode is $10\mathrm{mW}$, the value of series resistance ${R}_{s}$ to regulate the input unregulated supply is: 

Which of the following circuits is reverse - biased ?

In an alpha particle scattering experiment distance of closest approach for the $\alpha$ particle is $4.5 \times 10^{-14} \mathrm{~m}$. If target nucleus has atomic number 80 , then maximum velocity of $\alpha$ - particle is _______ $\times 10^5 \mathrm{~m} / \mathrm{s}$ approximately. $\left(\frac{1}{4 \pi \epsilon_0}=9 \times 10^9\right.$ SI unit, mass of $\alpha$ particle $\left.=6.72 \times 10^{-27} \mathrm{~kg}\right)$

The longest wavelength associated with Paschen series is : (Given $\mathrm{R}_{\mathrm{H}}=1.097 \times 10^7 \mathrm{SI}$ unit)

If three helium nuclei combine to form a carbon nucleus then the energy released in this reaction is _____$\times 10^{-2} \mathrm{MeV}$. (Given $1 \mathrm{u}=931 \mathrm{MeV} / \mathrm{c}^2$, atomic mass of helium $=4.002603 \mathrm{u}$ )

In a hypothetical fission reaction ${ }_{92} X^{236} \rightarrow{ }_{56} Y^{141}+{ }_{36} Z^{92}+3 R$ The identity of emitted particles ( $\mathrm{R})$ is :

A light emitting diode (LED) is fabricated using GaAs semiconducting material whose band gap is $1.42 \mathrm{eV}$. The wavelength of light emitted from the LED is :

The minimum energy required by a hydrogen atom in ground state to emit radiation in Balmer series is nearly :

Two sources of light emit with a power of $200W$. The ratio of number of photons of visible light emitted by each source having wavelengths $300\mathrm{nm}$ and $500\mathrm{nm}$ respectively, will be :

Conductivity of a photodiode starts changing only if the wavelength of incident light is less than $660\mathrm{nm}.$ The band gap of photodiode is found to be $(\frac{X}{8})\mathrm{eV}.$ The value of $X$ is: (Given $h=6.6\times {10}^{-34}Js,e=1.6\times {10}^{-19}C$)

An electron revolving in ${n}^{\text{th }}$ Bohr orbit has magnetic moment ${\mu }_{n}$. If ${\mu }_{n}\propto {n}^{x}$, the value of $x$ is:

A potential divider circuit is connected with a dc source of $20 \mathrm{~V}$, a light emitting diode of glow in voltage $1.8 \mathrm{~V}$ and a zener diode of breakdown voltage of $3.2 \mathrm{~V}$. The length (PR) of the resistive wire is $20 \mathrm{~cm}$. The minimum length of PQ to just glow the LED is _____$\mathrm{cm}$ 

The output of the given circuit diagram is 

The ratio of the shortest wavelength of Balmer series to the shortest wavelength of Lyman series for hydrogen atom is :

A nucleus at rest disintegrates into two smaller nuclei with their masses in the ratio of $2: 1$. After disintegration they will move :

The energy equivalent of $1 \mathrm{~g}$ of substance is :

Monochromatic light of frequency $6\times {10}^{14}\mathrm{Hz}$ is produced by a laser. The power emitted is $2\times {10}^{-3}W.$ How many photons per second on an average, are emitted by the source? (Given $h=6.63\times {10}^{-34}Js$)

The ratio of the magnitude of the kinetic energy to the potential energy of an electron in the ${5}^{\text{th }}$ excited state of a hydrogen atom is :

The shortest wavelength of the spectral lines in the Lyman series of hydrogen spectrum is $915 Ã…$. The longest wavelength of spectral lines in the Balmer series will be _____ $Ã…$.

Which figure shows the correct variation of applied potential difference (V) with photoelectric current (I) at two different intensities of light $\left(\mathrm{I}_1 < \mathrm{I}_2\right)$ of same wavelengths :

The correct truth table for the following logic circuit is :