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MCQOPTIONS
This section includes 12583 Mcqs, each offering curated multiple-choice questions to sharpen your Joint Entrance Exam - Main (JEE Main) knowledge and support exam preparation. Choose a topic below to get started.
| 2801. |
An atom emits a photon of wavelength X = 600 m by transition from an excited state of life time\[8\times {{10}^{-9}}s\]. If \[\Delta \,v\] represents the minimum uncertainty in the frequency of the photon, the fractional width \[\frac{\Delta v}{v}\] of the spectral line is of the order of |
| A. | \[{{10}^{-\,4}}\] |
| B. | \[{{10}^{-6}}\] |
| C. | \[{{10}^{-\,8}}\] |
| D. | \[{{10}^{-10}}\] |
| Answer» C. \[{{10}^{-\,8}}\] | |
| 2802. |
The photoelectric threshold wavelength of silver is \[3250\times {{10}^{-10}}m.\]The velocity of the electron ejected from a silver surface by ultraviolet light of wavelength \[2536\times {{10}^{-10\,}}\]m is (Given\[h=4.14\times {{10}^{-15}}eV\text{ and }c=3\times {{10}^{8}}m{{s}^{-1}}\]) |
| A. | \[=0.6\times {{10}^{6}}m{{s}^{-1}}\] |
| B. | \[=61\times {{10}^{3}}m{{s}^{-1}}\] |
| C. | \[=0.3\times {{10}^{6}}m{{s}^{-1}}\] |
| D. | \[=6\times {{10}^{6}}m{{s}^{-1}}\] |
| Answer» B. \[=61\times {{10}^{3}}m{{s}^{-1}}\] | |
| 2803. |
1.5 mW of 400 nm light is directed at a photoelectric cell. If 0.10 per cent of the incident photons produce photoelectrons, then find the current in the cell. |
| A. | \[4.8\mu A\] |
| B. | \[48\mu A\] |
| C. | \[1.8\mu A\] |
| D. | \[0.48\mu A\] |
| Answer» E. | |
| 2804. |
According to Einstein?s photoelectric equation, the plot of the kinetic energy of the emitted photo electrons from a metal Versus the frequency, of the incident radiation gives a straight line whose slope |
| A. | depends both on the intensity of the radiation and the metal used |
| B. | depends on the intensity of the radiation |
| C. | depends on the nature of the metal used |
| D. | is the same for the all metals and independent of the intensity of the radiation |
| Answer» E. | |
| 2805. |
A particle of mass M at rest decays into two particles of masses \[{{m}_{1}}\] and \[{{m}_{2}}\] having non-zero velocities. The ratio of the de Broglie wavelengths of the particles, \[{{\lambda }_{1}}/{{\lambda }_{2}},\] is |
| A. | \[{{m}_{1}}/{{m}_{2}}\] |
| B. | \[{{m}_{2}}/{{m}_{1}}\] |
| C. | 1 |
| D. | \[\sqrt{{{m}_{2}}}/\sqrt{{{m}_{1}}}\] |
| Answer» D. \[\sqrt{{{m}_{2}}}/\sqrt{{{m}_{1}}}\] | |
| 2806. |
When photons of wavelength \[{{\lambda }_{1}}\] are incident on an isolated sphere, the corresponding stopping potential is found to be V. When photons of wavelength \[{{\lambda }_{2}}\] are used, the corresponding stopping potential was thrice that of the above value. If light of wavelength \[{{\lambda }_{3}}\] is used then find the stopping potential for this case: |
| A. | \[\frac{hc}{e}\left[ \frac{1}{{{\lambda }_{3}}}+\frac{1}{{{\lambda }_{2}}}-\frac{1}{{{\lambda }_{1}}} \right]\] |
| B. | \[\frac{hc}{e}\left[ \frac{1}{{{\lambda }_{3}}}+\frac{1}{2{{\lambda }_{2}}}-\frac{1}{{{\lambda }_{1}}} \right]\] |
| C. | \[\frac{hc}{e}\left[ \frac{1}{{{\lambda }_{3}}}-\frac{1}{{{\lambda }_{2}}}-\frac{1}{{{\lambda }_{1}}} \right]\] |
| D. | \[\frac{hc}{e}\left[ \frac{1}{{{\lambda }_{3}}}+\frac{1}{2{{\lambda }_{2}}}-\frac{3}{2{{\lambda }_{1}}} \right]\] |
| Answer» E. | |
| 2807. |
Two identical photocathodes receive light of frequencies \[{{f}_{1}}\] and\[{{f}_{2}}\]. If the velocities of the photo electrons (of mass m) coming out are respectively |
| A. | \[v_{1}^{2}-v_{2}^{2}=\frac{2h}{m}\left( {{f}_{1}}-{{f}_{2}} \right)\] |
| B. | \[{{v}_{1}}+{{v}_{2}}={{\left[ \frac{2h}{m}\left( {{f}_{1}}+{{f}_{2}} \right) \right]}^{1/2}}\] |
| C. | \[v_{1}^{2}+v_{2}^{2}=\frac{2h}{m}\left( {{f}_{1}}+{{f}_{2}} \right)\] |
| D. | \[{{v}_{1}}-{{v}_{2}}={{\left[ \frac{2h}{m}\left( {{f}_{1}}-{{f}_{2}} \right) \right]}^{1/2}}\] |
| Answer» B. \[{{v}_{1}}+{{v}_{2}}={{\left[ \frac{2h}{m}\left( {{f}_{1}}+{{f}_{2}} \right) \right]}^{1/2}}\] | |
| 2808. |
The threshold wavelength of the tungsten is 2300 If ultraviolet light of wavelength \[1800\text{ }\overset{\text{o}}{\mathop{\text{A}}}\,\] is incident on it, then the maximum kinetic energy of photoelectrons would be about |
| A. | 1.49eV |
| B. | 2.2eV |
| C. | 3.0eV |
| D. | 5.0eV |
| Answer» B. 2.2eV | |
| 2809. |
When X-rays of wavelength 0.5 A would be transmitted by an aluminum tube of thickness 7 mm, its intensity remains one-fourth. The absorption coefficient of aluminum for these X-rays is |
| A. | \[0.188m{{m}^{-1}}\] |
| B. | \[0.189m{{m}^{-1}}\] |
| C. | \[0.198m{{m}^{-1}}\] |
| D. | None of these |
| Answer» D. None of these | |
| 2810. |
Thickness of the medium \[(\mu )\] at which intensity of emergent x-rays becomes half is: |
| A. | \[\frac{1.23}{\mu }\] |
| B. | \[\frac{3.318}{\mu }\] |
| C. | \[\frac{0.126}{\mu }\] |
| D. | \[\frac{0.693}{\mu }\,\] |
| Answer» E. | |
| 2811. |
Electrons with energy 80 keV are incident on the tungsten target of an X-ray tube. K-shell electrons of tungsten have 72.5 keV energy. X- rays emitted by the tube contain only |
| A. | a continuous X-ray spectrum (Bremsstrahlung) with a minimum wavelength of \[\text{0}\text{.155}\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| B. | a continuous X-ray spectrum (Bremsstrahlung) with all wavelengths |
| C. | the characteristic X-ray spectrum of tungsten |
| D. | a continuous X-ray spectrum (Bremsstrahlung) with a minimum wavelength of \[\text{0}\text{.155}\overset{\text{o}}{\mathop{\text{A}}}\,\]and the characteristic X-ray spectrum of tungsten.. |
| Answer» E. | |
| 2812. |
An X-ray tube is operated at 15 kV. Calculate the upper limit of the speed of the electrons striking the target. |
| A. | \[7.26\times {{10}^{7}}m/s\] |
| B. | \[7.62\times {{10}^{7}}m/s\] |
| C. | \[7.62\times {{10}^{7}}cm/s\] |
| D. | \[7.26\times {{10}^{9}}m/s.\] |
| Answer» B. \[7.62\times {{10}^{7}}m/s\] | |
| 2813. |
The short wavelength limit of continuous X-radiation emitted by an X-ray tube operating at 30 kV is 0.414 A. Calculate Planck's constant. |
| A. | \[\text{6}\text{.22 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-34}}}\text{erg-sec}\] |
| B. | \[\text{6}\text{.624 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-24}}}\text{erg-sec}\] |
| C. | \[\text{6}\text{.624 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-27}}}\text{J-sec}\] |
| D. | \[\text{6}\text{.624 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-34}}}\text{J-sec}\] |
| Answer» E. | |
| 2814. |
A proton and a deuteron are accelerated through the same accelerating potential. Which one of the two has greater value of de-Broglie wavelength associated with it, and less momentum? |
| A. | Proton |
| B. | Deutron |
| C. | Both have equal values |
| D. | None of these |
| Answer» B. Deutron | |
| 2815. |
The energy in monochromatic X-rays of wavelength 1 A is roughly equal to |
| A. | \[2\times {{10}^{-15}}J\] |
| B. | \[2\times {{10}^{-16}}J\] |
| C. | \[2\times {{10}^{-17}}J\] |
| D. | \[2\times {{10}^{-18}}J\] |
| Answer» B. \[2\times {{10}^{-16}}J\] | |
| 2816. |
A horizontal cesium plate (work function = 1.9 eV) is moved vertically downward at a constant speed V in a room full of radiation of wavelength 250 nm and above. The minimum value of v so that the vertically upward component of velocity is no positive for each photoelectron. |
| A. | \[1.04\times {{10}^{6}}m{{s}^{-1}}\] |
| B. | \[2.03\times {{10}^{7}}m{{s}^{-1}}\] |
| C. | \[4.03\times {{10}^{8}}m{{s}^{-1}}\] |
| D. | \[5.11\times {{10}^{9}}m{{s}^{-1}}\] |
| Answer» B. \[2.03\times {{10}^{7}}m{{s}^{-1}}\] | |
| 2817. |
The potential difference applied to an X-ray tube is 5kV and the current through it is 3.2mA. Then the number of electrons striking the target per second is |
| A. | \[2\times {{10}^{16}}\] |
| B. | \[5\times {{10}^{6}}\] |
| C. | \[5\times {{10}^{6}}\] |
| D. | \[4\times {{10}^{15}}\] |
| Answer» B. \[5\times {{10}^{6}}\] | |
| 2818. |
When the minimum wavelength of X-rays is 2A then the applied potential difference between cathode and anticathode will be |
| A. | 6.2kV |
| B. | 2.48 kV |
| C. | 24.8kV |
| D. | 62kV |
| Answer» B. 2.48 kV | |
| 2819. |
A parallel beam of electrons travelling in x-direction falls on a slit of width d (see figure). If after passing the slit, an electron acquires momentum p in the y-direction then for a majority of electrons passing through the slit (h is Planck's constant): |
| A. | \[|{{P}_{y}}|>h\] |
| B. | \[|{{P}_{y}}|<h\] |
| C. | \[|{{P}_{y}}|=h\] |
| D. | \[|{{P}_{y}}|>>h\,\] |
| Answer» B. \[|{{P}_{y}}|<h\] | |
| 2820. |
An x-ray tube is operating at 30 KV then the minimum wavelength of the x-rays coming out of the tube is - |
| A. | \[1.24\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| B. | \[0.413\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| C. | \[124\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| D. | \[0.13\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| Answer» C. \[124\overset{\text{o}}{\mathop{\text{A}}}\,\] | |
| 2821. |
The ratio of energies of X-rays of the wavelength \[\text{0}\text{.01}\overset{\text{o}}{\mathop{\text{A}}}\,\]and \[\text{0}\text{.5}\overset{\text{o}}{\mathop{\text{A}}}\,\] will be |
| A. | 1:1 |
| B. | 1:2 |
| C. | 1:5 |
| D. | 2.08402777777778 |
| Answer» E. | |
| 2822. |
Which one of the following statements is WRONG in the context of X-rays generated from an X-ray tube? |
| A. | Wavelength of characteristic X-rays decreases when the atomic number of the target increases. |
| B. | Cut-off wavelength of the continuous X-rays depends on the atomic number of the target |
| C. | Intensity of the characteristic X-rays depends on the electrical power given to the X-ray tube |
| D. | Cut-off wavelength of the continuous X-rays depends on the energy of the electrons in the X-ray tube |
| Answer» C. Intensity of the characteristic X-rays depends on the electrical power given to the X-ray tube | |
| 2823. |
When the X-ray tube is operated at 1kV, then X- rays of minimum wavelength \[\text{6}\text{.22 }\overset{\text{o}}{\mathop{\text{A}}}\,\] are produced. If the tube is operated at 10 kV, then the minimum wavelength of x-rays will be |
| A. | \[\text{0}\text{.622 }\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| B. | \[\text{6}\text{.22 }\overset{\text{o}}{\mathop{\text{A}}}\,\,\] |
| C. | \[\text{3}\text{.11 }\overset{\text{o}}{\mathop{\text{A}}}\,\,\] |
| D. | zero |
| Answer» B. \[\text{6}\text{.22 }\overset{\text{o}}{\mathop{\text{A}}}\,\,\] | |
| 2824. |
An electron of mass 'm' and charge 'e' initially at rest gets accelerated by a constant electric field E. The rate of change of de-Broglie wavelength of this electron at time t, ignoring relativistic effects is: |
| A. | \[\frac{-h}{eE{{t}^{2}}}\] |
| B. | \[\frac{-eht}{E}\] |
| C. | \[\frac{-mh}{eE{{t}^{2}}}\] |
| D. | \[\frac{-h}{eE}\] |
| Answer» B. \[\frac{-eht}{E}\] | |
| 2825. |
The maximum kinetic energy of the electrons hitting a target so as to produce X-ray of wavelength 1 A is |
| A. | 1.24keV |
| B. | 12.4keV |
| C. | 124keV |
| D. | None of these |
| Answer» C. 124keV | |
| 2826. |
In a photo-emissive cell, with exciting wavelength\[\lambda \], the maximum kinetic energy of electron is K. If the exciting wavelength is changed to \[3\lambda /4\] the kinetic energy of the fastest emitted electron will be |
| A. | 3K/4 |
| B. | 4K/3 |
| C. | less than 4K/3 |
| D. | greater than 4K/3 |
| Answer» E. | |
| 2827. |
A photoelectric cell is illuminated by a point source of light 1m away. When the source is shifted to 2m then |
| A. | number of electrons emitted is a quarter of the in ideal number |
| B. | each emitted electron carries one quarter of the initial energy |
| C. | number of electrons emitted is half the initial number |
| D. | each emitted electron carries half the initial energy |
| Answer» B. each emitted electron carries one quarter of the initial energy | |
| 2828. |
The cathode of a photoelectric cell is changed such that the work function changes from \[{{W}_{1}}\] to \[{{W}_{2}}({{W}_{2}}>{{W}_{1}}).\] If the current before and after changes are \[{{I}_{1}}\] and \[{{I}_{2}}\]. all other conditions remaining unchanged, then (assuming \[hv>{{W}_{2}}\]) |
| A. | \[{{I}_{1}}={{I}_{2}}\] |
| B. | \[{{I}_{1}}<{{I}_{2}}\] |
| C. | \[{{I}_{1}}>{{I}_{2}}\] |
| D. | \[{{I}_{1}}<{{I}_{2}}<2{{I}_{1}}\] |
| Answer» B. \[{{I}_{1}}<{{I}_{2}}\] | |
| 2829. |
A source of light is placed at a distance of 50 cm from a photocell and the stopping potential is found to be \[{{V}_{0}}\]. If the distance between the light source and photocell is made 25 cm, the new stopping potential will be |
| A. | \[2{{V}_{0}}\] |
| B. | \[{{V}_{0}}/2\] |
| C. | \[{{V}_{0}}\] |
| D. | \[4{{V}_{0}}\] |
| Answer» D. \[4{{V}_{0}}\] | |
| 2830. |
A sensor is exposed for time t to a lamp of power P placed at a distance l. The sensor has an opening that is 4d in diameter. Assuming all energy of the lamp is given off as light, the number of photons entering the sensor if the wavelength of light is X is |
| A. | \[N=P\lambda {{d}^{2}}t/hc{{l}^{2}}\] |
| B. | \[N=4P\lambda {{d}^{2}}t/hc{{l}^{2}}\] |
| C. | \[N=P\lambda {{d}^{2}}t/4hc{{l}^{2}}\] |
| D. | \[N=P\lambda {{d}^{2}}t/16hc{{l}^{2}}\] |
| Answer» B. \[N=4P\lambda {{d}^{2}}t/hc{{l}^{2}}\] | |
| 2831. |
The fastest photoelectrons emitted from a metallic surface during the photoelectric effect have an energy of 8eV. The same photons when incident on atomic hydrogen, are strongly absorbed, exciting the atoms from the ground state to the first excited state. The work function of the metal is |
| A. | 5.6eV |
| B. | 2.2eV |
| C. | 4.6eV |
| D. | 11.4eV |
| Answer» C. 4.6eV | |
| 2832. |
The work functions of metals A and B are in the ratio 1 : 2. If light of frequencies f and 2f are incident on the surfaces of A and B respectively, the ratio of the maximum kinetic energies of photoelectrons emitted is (f is greater than threshold frequency of A, 2f is greater than threshold frequency of B) |
| A. | 0.0423611111111111 |
| B. | 1 : 2 |
| C. | 1 : 3 |
| D. | 0.0444444444444444 |
| Answer» C. 1 : 3 | |
| 2833. |
A 5 watt source emits monochromatic light of wavelength\[\text{5000 }\overset{\text{o}}{\mathop{\text{A}}}\,\]. When placed 0.5 m away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of 1.0 m, the number of photoelectrons liberated will be reduced by a factor of |
| A. | 8 |
| B. | 16 |
| C. | 2 |
| D. | 4 |
| Answer» E. | |
| 2834. |
Electrons are accelerated through a potential difference V and protons are accelerated through a potential difference 4 V. The de-Broglie wavelengths are \[{{\lambda }_{e}}\] and \[{{\lambda }_{p}}\] for electrons and protons respectively. The ratio of \[\frac{{{\lambda }_{e}}}{{{\lambda }_{p}}}\]is given by: (given \[{{m}_{e}}\]is mass of electron and \[{{m}_{p}}\]is mass of proton) |
| A. | \[\sqrt{\frac{{{m}_{p}}}{{{m}_{e}}}}\] |
| B. | \[\sqrt{\frac{{{m}_{e}}}{{{m}_{p}}}}\] |
| C. | \[\frac{1}{2}\sqrt{\frac{{{m}_{e}}}{{{m}_{p}}}}\] |
| D. | \[2\sqrt{\frac{{{m}_{e}}}{{{m}_{p}}}}\] |
| Answer» E. | |
| 2835. |
A photon of frequency/causes the emission of a photoelectron of maximum kinetic energy \[{{E}_{k}}\] from a metal. If a photon of frequency 3f is incident on the same metal, the maximum kinetic energy of the emitted photoelectron |
| A. | equals \[3{{E}_{k}}\] |
| B. | is greater than \[3{{E}_{k}}\] |
| C. | is less than \[3{{E}_{k}}\] |
| D. | may be equal to, less than or, greater than \[3{{E}_{k}}\] |
| Answer» C. is less than \[3{{E}_{k}}\] | |
| 2836. |
An \[\alpha \]-particle having a de-Broglie wavelength \[{{\lambda }_{i}}\] collides with a stationary carbon nucleus. The \[\alpha \]-particle moves off in a different direction as shown below. After the collision, the de Broglie wavelengths of the \[\alpha \]-particle and the carbon nucleus are \[{{\lambda }_{f}}\] and \[{{\lambda }_{e}}\] respectively. Which of the following relations about de Broglie wavelengths is correct |
| A. | \[{{\lambda }_{i}}<{{\lambda }_{f}}\] |
| B. | \[{{\lambda }_{i}}>{{\lambda }_{f}}\] |
| C. | \[{{\lambda }_{f}}={{\lambda }_{i}}\] |
| D. | \[{{\lambda }_{i}}={{\lambda }_{e}}\] |
| Answer» B. \[{{\lambda }_{i}}>{{\lambda }_{f}}\] | |
| 2837. |
A point source of light is placed at the centre of curvature of a hemispherical surface. The radius of curvature is R and the inner surface is completely reflecting The force on the hemisphere due to the light falling on it if the source emits a power P [c is the speed of light ] |
| A. | \[\frac{2P}{C}\] |
| B. | \[\frac{P}{2C}\] |
| C. | \[\frac{5P}{2C}\,\] |
| D. | \[\frac{4P}{3C}\,\] |
| Answer» B. \[\frac{P}{2C}\] | |
| 2838. |
A mono chromatic source of light operating at 400 w emits \[8\times {{10}^{20}}\] photons per second, the wavelength of light is |
| A. | 100nm |
| B. | 200nm |
| C. | 300nm |
| D. | 400nm |
| Answer» E. | |
| 2839. |
A particle A of mass m and initial velocity v m collides with a particle B of mass \[\frac{m}{2}\] which is at rest. The collision is head on, and elastic. The ratio of the de-Broglie wavelengths \[{{\lambda }_{A}}\] to \[{{\lambda }_{B}}\] after the collision is |
| A. | \[\frac{2}{3}\] |
| B. | \[\frac{1}{2}\] |
| C. | \[\frac{1}{3}\] |
| D. | \[2\] |
| Answer» E. | |
| 2840. |
Radiation of wavelength \[\lambda \], is incident on a photocell. The fastest emitted electron has speed v. If the wavelength is changed to \[\frac{3\lambda }{4}\], the speed of the fastest emitted electron will be: |
| A. | \[=v{{\left( \frac{4}{3} \right)}^{\frac{1}{2}}}\] |
| B. | \[=v{{\left( \frac{3}{4} \right)}^{\frac{1}{2}}}\] |
| C. | \[>v{{\left( \frac{4}{3} \right)}^{\frac{1}{2}}}\] |
| D. | \[<v{{\left( \frac{4}{3} \right)}^{\frac{1}{2}}}\] |
| Answer» D. \[<v{{\left( \frac{4}{3} \right)}^{\frac{1}{2}}}\] | |
| 2841. |
A cylindrical rod of some laser material \[5\times {{10}^{-2}}m\] long and \[{{10}^{-2}}\] m in diameter contains \[2\times {{10}^{25}}\] ions \[6.6\times {{10}^{-7}}m.\] per m3. If on excitation all the ions are in the upper energy level and de-excite simultaneously emitting photons in the same direction, calculate the maximum energy contained in a pulse of radiation of wavelength \[6.6\times {{10}^{-7}}m.\] If the pulse lasts for\[{{10}^{-7}}s\]. the average power of the laser during the pulse is |
| A. | 532 MW |
| B. | 352 MW |
| C. | 235MW |
| D. | 325 MW |
| Answer» D. 325 MW | |
| 2842. |
Light of wavelength 180 nm ejects photoelectron from a plate of a metal whose work function is 2 eV. If a uniform magnetic field of \[5\times {{10}^{-5}}T\] is applied parallel to plate, what would be the radius of the path followed by electrons ejected normally from the plate with maximum energy? |
| A. | 1.239 m |
| B. | 0.149 m |
| C. | 3.182 m |
| D. | 2.33 m |
| Answer» C. 3.182 m | |
| 2843. |
The potential energy of a particle of mass m is given by \[V\left( x \right)=\left\{ \begin{matrix} {{E}_{0}}; & 0\le x\le 1 \\ 0; & x>1 \\ \end{matrix} \right\}\]\[{{\lambda }_{1}}\] and \[{{\lambda }_{2}}\]are the de-Broglie wavelengths of the particle, when \[0\le x\le 1\] and \[x>1\]respectively. If the total energy of particle is\[2{{E}_{0}}\], find \[{{\lambda }_{1}}/{{\lambda }_{2}}\]. |
| A. | \[\sqrt{2}\] |
| B. | \[\sqrt{3}\] |
| C. | \[\sqrt{5}\] |
| D. | \[2\sqrt{2}\] |
| Answer» B. \[\sqrt{3}\] | |
| 2844. |
Find the frequency of light which ejects electrons from a metal surface fully stopped by a retarding potential of 3V. The photoelectric effect begin in this metal at frequency of \[6\times {{10}^{14}}\] per second. |
| A. | \[1.32\times {{10}^{15}}Hz\] |
| B. | \[3.28\times {{10}^{14}}Hz\] |
| C. | \[6.22\times {{10}^{15}}Hz\] |
| D. | \[2.22\times {{10}^{11}}Hz\] |
| Answer» B. \[3.28\times {{10}^{14}}Hz\] | |
| 2845. |
When a surface is irradiated with light of wavelength \[4950\overset{\text{o}}{\mathop{\text{A}}}\,\], a photocurrent appears which vanishes if a retarding potential greater than 0.6 V is applied across the photo tube. When a different source of light is used, it is found that the critical retarding potential is changed to 1.1 V. Find the wavelength of second source. |
| A. | \[\text{4077}\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| B. | \[992\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| C. | \[628\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| D. | \[238\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| Answer» B. \[992\overset{\text{o}}{\mathop{\text{A}}}\,\] | |
| 2846. |
When a beam of 10.6 eV photons of intensity \[2.0\text{ }W/{{m}^{2}}\,\] falls on a platinum surface of area \[1.0\times {{10}^{-4}}{{m}^{2}}\] and work function 5.6 eV, 0.53% of the incident photons eject photoelectrons, then the number of photoelectrons emitted per second and their minimum & maximum energies (in eV) [Take \[1eV=1.6\times {{10}^{-19}}J\]] are respectively. |
| A. | \[1.18\times {{10}^{10}},2eV,5eV\] |
| B. | \[1.18\times {{10}^{14}},0eV,5eV\] |
| C. | \[2.18\times {{10}^{13}},0eV,5eV\] |
| D. | \[3.11\times {{10}^{11}},1eV,5eV\] |
| Answer» C. \[2.18\times {{10}^{13}},0eV,5eV\] | |
| 2847. |
Assume that the de Broglie wave associated with an electron can form a standing wave between the atoms arranged in a one dimensional array with nodes at each of the atomic sites. It is found that one such standing wave is formed if the distance d between the atoms of the array is \[2\overset{\text{o}}{\mathop{\text{A}}}\,\]A similar standing wave is again formed if d is increased to \[2.5\overset{\text{o}}{\mathop{\text{A}}}\,\]but not for any intermediate value of d. The energy of the electrons in electron volt and the least value of d for which the standing wave of the type described above can form, respectively are |
| A. | 112eV, \[1.5\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| B. | 151eV, \[0.5\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| C. | 211eV, \[1.5\overset{\text{o}}{\mathop{\text{A}}}\,\] |
| D. | None of these |
| Answer» C. 211eV, \[1.5\overset{\text{o}}{\mathop{\text{A}}}\,\] | |
| 2848. |
An electron of mass m and a photon have same energy E. The ratio of de-Broglie wavelengths associated with them is: |
| A. | \[\frac{1}{c}{{\left( \frac{E}{2m} \right)}^{\frac{1}{2}}}\] |
| B. | \[{{\left( \frac{E}{2m} \right)}^{\frac{1}{2}}}\] |
| C. | \[c{{\left( 2mE \right)}^{\frac{1}{2}}}\] |
| D. | \[\frac{1}{xc}{{\left( \frac{E}{2m} \right)}^{\frac{1}{2}}}\] |
| Answer» B. \[{{\left( \frac{E}{2m} \right)}^{\frac{1}{2}}}\] | |
| 2849. |
A particle of mass m is projected from ground with velocity u making angle \[\theta \] with the vertical. The de-Broglie wavelength of the particle at the highest point is - |
| A. | \[\infty \] |
| B. | \[\frac{h}{mu\sin \theta }\] |
| C. | \[\frac{h}{mu\cos \theta }\] |
| D. | \[\frac{h}{mu}\] |
| Answer» C. \[\frac{h}{mu\cos \theta }\] | |
| 2850. |
A homogeneous ball (mass = m) of ideal black material at rest is illuminated with a radiation having a set of photons (wavelength = X), each with the same momentum and the same energy. The rate at which photons fall on the ball is n. The linear acceleration of the ball is |
| A. | \[m\lambda /nh\] |
| B. | \[nh/m\lambda \] |
| C. | \[nh/m\lambda \] |
| D. | \[2m\lambda /nh\] |
| Answer» C. \[nh/m\lambda \] | |