Stopping Potential

Q.

Define stopping potential.

Q. The maximum kinetic energy of photoelectrons emitted from a surface when photons of energy 6 eV fall on it is 4 eV. the stopping potential in volts is

1. 2
2. 4
3. 6
4. 10

Q. Assertion : When the speed of an electron increases its specific charge decreases.

Reason: Specific charge is the ratio of the charge to mass.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.

2. Both assertion and reason are true but reason is not the correct explanation of the assertion.

3. Assertion is true but reason is false.

4. Assertion and reason both are false.

5. Assertion is false but reason is true.

Q. When a monochromatic point source of light is at a distance of 0.2 m from a photoelectric cell, the cut-off voltage and the saturation current are, respectively, 0.6 V and 18.0 mA. If the same source is placed 0.6 m away from the photoelectric cell, then

1. The stopping potential will be 0.2 V
2. The stopping potential will be 0.6 V
3. The saturation current will be 6.0 mA
4. The saturation current will be 2.0 mA

Q. In a photo electric emission process from a metal of work function 1.8 eV, the kinetic energy of most energetic electrons is 0.5 eV. The corresponding stopping potential is

1. 1.8 V
2. 1.3 V
3. 0.5 V
4. 2.3 V

Q.

Light of two different frequencies whose photons have energies 1 eV and 2.5 eV respectively, successively illuminate a metallic surface whose work function is 0.5 eV. Ratio of maximum speeds of emitted electrons will be

1. 1:2

2. 1:5

3. 1:1

4. 1:4

Q. Work function of caesium is $2.14eV$. What is the wavelength of incident light if photocurrent is brought to zero by a stopping potential of $0.6V$?

1. $454nm$
2. $113nm$
3. $906nm$
4. $226nm$

Q.

How is rms value of AC voltage related to peak value of AC voltage

Q. The work function of caesium metal is 2.14 eV. When light of frequency 6 ×1014Hz is incident on the metal surface, photoemission of electrons occurs. What is the (a) maximum kinetic energy of the emitted electrons, (b) Stopping potential, and (c) maximum speed of the emitted photoelectrons?

Q. A particle of mass $1\text{mg}$ has the same de-Broglie wavelength as that of an electron moving with a velocity of $3\times {10}^6{\text{ms}}^{-1}$. The velocity of the particle is,
$[$ Take mass of electron, $m_e=9.1\times {10}^{-31}\text{kg}]$

1. $3\times {10}^{-21}{\text{ms}}^{-1}$
2. $2.7\times {10}^{-21}{\text{ms}}^{-1}$
3. $2.7\times {10}^{-18}{\text{ms}}^{-1}$
4. $3\times {10}^{-18}{\text{ms}}^{-1}$

Q. A narrow electron beam passes undeviated through an electric field $E=3\times {10}^4\text{volt/m}$ and an overlapping magnetic field $B=2\times {10}^{-3}{\text{W/m}}^2$. If electric field and magnetic field are mutually perpendicular. The speed of the electrons is

1. $0.67\times {10}^{-7}\text{m/s}$
2. $60\text{m/s}$
3. $10.3\times {10}^7\text{m/s}$
4. $1.5\times {10}^7\text{m/s}$

Q. When a point source of light is at a distance of 50 cm from a photoelectric cell, the cut off voltage is found to be $V_0$. If the same source is placed at a distance of 1 m from the cell, the cut off voltage will be

1. $2V_0$
2. $\frac{V_0}{4}$
3. $\frac{V_0}{2}$
4. $V_0$

Q.

In an X-ray tube, electrons emitted from a filament (cathode) carrying current $I$ hit a target (anode) at a distance $d$ from the cathode. The target is kept at a potential $V$ higher than the cathode resulting in the emission of continuous and characteristic X-rays. If the filament current $I$ is decreased to $\frac{1}{2}$, the potential difference $V$ is increased to $2V$, and the separation distance $d$ is reduced to $\frac{d}{2}$, then

1. The cut-off wavelength will reduce to half, and the wavelengths of the characteristic X-rays will remain the same

2. The cut-off wavelength, as well as the wavelengths of the characteristic X-rays, will remain the same

3. The cut-off wavelength will reduce to half, and the intensities of all the X-rays will decrease

4. The cut-off wavelength will become two times larger, and the intensity of all the X-rays will decrease

Q.

An electron in a hydrogen atom undergoes a transition from an orbit with quantum number $n_i$ to another with quantum number $n_f$. $V_i$ and $V_f$ are respectively the initial and final potential energies of the electron. If $\frac{V_f}{V_i}=6.25$, then the smallest possible $n_f$ is

Q. When light of frequency twice the threshold frequency is incident on the metal plate, the maximum velocity of emitted electron is $v_1$. When the frequency of incident radiation is increased to five times the threshold value, the maximum velocity of emitted electron becomes $v_2$. If $v_2=x{v}_1$, the value of $x$ will be

Q. In photoelectric experiment, the collector plate is at 2V with respect to emitter plate(phi= 4.5eV). The emitter is illuminated by a source of monochromatic light of wavelength 200nm. The minimum and maximum kinetic energy of photoelectrons reaching collector is: 1. 0, 1.7eV 2. 2eV, 3.7eV 3. 1.5eV, 4.3eV 4. 3eV, 5.2eV Give the solution also

Q. Radiation of wavelength $\lambda$ is incident on a photocell. The fastest emitted electron has a speed $v$. If the wavelength is changed to $\frac{3\lambda }{4}$, the speed of the fastest emitted electron will be :

1. $>v{\left(\frac{4}{3}\right)}^{1/2}$
2. $<v{\left(\frac{4}{3}\right)}^{1/2}$
3. $=v{\left(\frac{4}{3}\right)}^{1/2}$
4. $=v{\left(\frac{3}{4}\right)}^{1/2}$

Q. If photons of frequency v are incident on the surface of metal A and B of Threshold frequency v/2 and v/3 respectively the ratio of maximum kinetic energy of electrons emitted from A to B is

Q. Sketch the graphs showing variation of stopping potential with frequency of incident radiations for two photosensitive materials A and B having threshold frequencies $v_A>v_B$.

(i) In which case is the stopping potential more and why ?

(ii) Does the slope of the graph depend on the nature of the material used ? Explain.

Q. When photons of wavelength ${\lambda }_1$ are incident on a metal plate, the corresponding stopping potential is found to be $V$. When photons of wavelength ${\lambda }_2$ are used, the corresponding stopping potential was thrice the above value. If light of wavelength ${\lambda }_3$ is used, the stopping potential for wavelength ${\lambda }_3$ in terms of ${\lambda }_1$ and ${\lambda }_2$ will be

1. $\frac{hc}{e}\left(\frac{1}{{\lambda }_3}+\frac{1}{{\lambda }_2}-\frac{1}{{\lambda }_1}\right]$
2. $\frac{hc}{e}\left(\frac{1}{{\lambda }_3}-\frac{1}{{\lambda }_2}-\frac{1}{{\lambda }_1}\right]$
3. $\frac{hc}{e}\left(\frac{1}{{\lambda }_3}+\frac{1}{2{\lambda }_2}-\frac{1}{{\lambda }_1}\right]$
4. $\frac{hc}{e}\left(\frac{1}{{\lambda }_3}+\frac{1}{2{\lambda }_2}-\frac{3}{2{\lambda }_1}\right]$

Q. A metal whose work function is $3.3eV$ is illuminated by light of wavelength $3\times {10}^{-7}$ m. What is the threshold frequency for photoelectric emission? Given Planck's constant $=6.6\times {10}^{-34}Js$.

1. $0.4\times {10}^{15}Hz$
2. $0.8\times {10}^{15}Hz$
3. $1.6\times {10}^{15}Hz$
4. $3.2\times {10}^{15}Hz$
   

Q. The following graph shows the variation of photocurrent for a photosensitive metal:

(a) Identify the variable X on the horizontal axis.
(b) What does the point A on the horizontal axis represent?
(c) Draw this graph for three different values of frequencies of incident radiation $v_1,v_2,and{v}_3(v_1>v_2>v_3)$ for same intensity.
(d) Draw this graph for three different values of intensities of incident radiation $I_1,I_{2}and{I}_3(I_1>I_2>I_3)$ having same frequency.

Q.

A beam of electrons of energy $\mathrm{E}$ scatters from a target having atomic spacing $1\stackrel{\circ }{\mathrm{A}}.$The first maximum intensity occurs at $\mathrm{\theta }=60°$ Then $\mathrm{E}$ (in eV) is __________.

(Planck constant $6.64\times {10}^{-34}\mathrm{js},1\mathrm{eV}=1.6\times {10}^{-19}\mathrm{Js},1\mathrm{eV}=1.6\times {10}^{-19}\mathrm{J},$electron mass m=$9.1\times {10}^{-31}\mathrm{kg}$)

Q. The graphs show the variation of current $I$ (y -axis) in two photocells A & B as a function of the applied voltage $V$ (x -axis), when light of same frequency is incident on the cell. Which of the following is the correct conclusion drawn from the data?

1. Cathodes of the two cells are made from the same substance, the intensity of light used are different
2. Cathode substances as well as intensity of ligth are different
3. Cathodes are made from differnet substances and the intensity of light is the same
4. No conclusion can be drawn

Q.

A small piece of cesium metal ($\varphi =1.9eV$) is kept at a distance of 20 cm from a large metal plate having a charge density of 1.0 $\times {10}^{-2}C{m}^{-2}$ on the surface facing the cesium piece. A monochromatic light of wavelength 400 nm is incident on the cesium piece. Find the minimum and the maximum kinetic energy of the photo electrons reaching the large metal plate. Neglect any change in electric field due to the small piece of cesium present.

Q. An electron is accelerated under a potential difference of 182 V. The maximum velocity of electron will be (charge of electron is $1.6\times {10}^{-19}C$and its mass is $9.1\times {10}^{-31}kg$)

1. $800m{s}^{-1}$
2. $8\times {10}^{6}m{s}^{-1}$
3. $4\times {10}^{3}m{s}^{-1}$
4. $4\times {10}^{6}m{s}^{-1}$

Q. The linear momentum of an electron, initially at rest, accelerated through a potential difference of 100 V is (in kg $m{s}^{-1}$)

1. $2.25\times {10}^7$
2. $5.4\times {10}^7$
3. $2.85\times {10}^{-24}$
4. $5.4\times {10}^{-24}$

Q. A gas containing hydrogen like ions with atomic no. Z, emits photons in transition $n+2\to n$, where $n=Z$. These photons fall on a metallic plate and eject electrons having minimum de-Broglie wavelength $\lambda$ of $5A^{\circ }$. Find the value of $‘Z^{\prime }$ if the work function of metal is $4.2\text{eV}$.

Q.

Find out the longest wavelength of absorption line for hydrogen gas-containing atoms in the ground state.

Q. Monochromatic light of frequency ${\nu }_1$ irradiates a photocell and the stopping potential is found to be $V_1$. What is the new stopping potential of the cell if it is irradiated by monochromatic light of frequency ${\nu }_2$?

1. $V_1-\frac{h}{e}({\nu }_2-{\nu }_1)$
2. $V_1+\frac{h}{e}({\nu }_2-{\nu }_1)$
3. $V_1+\frac{h}{e}({\nu }_1+{\nu }_2)$
4. $V_1-\frac{h}{e}({\nu }_1+{\nu }_2)$