Physics - Dual Nature of Matter and Radiation
Exam Duration: 45 Mins Total Questions : 30
A photon of energy E is incident on a photosensitive substance of work function \(\phi \) such that \(E<\phi \). Consider the two statements
I. Photoelectric effect necessarily takes place
II. The excess energy (in the form of KE) of the emitted electron is exactly \(E-\phi \)
- (a)
Both (I) and (II) are correct
- (b)
(I) is correct but not (II)
- (c)
(II) is correct but not (I)
- (d)
Both (I) and (II) are incorrect.
The act of photoelectric effect taking place with a certain photosensitive metal depends upon (I) frequency and (II) intensity of the incident radiation.
- (a)
Both (I) and (II) are correct
- (b)
Only (I) is correct
- (c)
Only (II) is correct
- (d)
Neither (I) nor (II) is correct
Monochromatic light with a frequency well above the cut-off frequency is incident on the emitter in a photoelectric effect apparatus. The frequency of the light is then doubled while the intensity is kept constant. How does this affect the photoelectric current?
- (a)
The photoelectric current will increase
- (b)
The photoelectric current will decrease
- (c)
The photoelectric current will remain the same
- (d)
None of the above
A point source of light is used in a photoelectric effect. If the source is removed farther from the emitting metal, then the stopping potential.
- (a)
will increase
- (b)
will decrease
- (c)
will remain constant
- (d)
will either increase or decrease
If the frequency of light in a photoelectric experiment is doubled, then stopping potential will
- (a)
be doubled
- (b)
halved
- (c)
become more than double
- (d)
become less than double
Let K1 be the maximum kinetic energy of photoelectrons emitted by a light of wavelength \({ \lambda }_{ 1 }\) and K2 corresponding to \({ \lambda }_{ 2 }\). If \({ \lambda }_{ 1 }=2{ \lambda }_{ 2 }\), then
- (a)
2K1 = K2
- (b)
K1 = 2K2
- (c)
K1 < K2/2
- (d)
K1 > 2K2
Radiation of two photon energies twice and five times the work function of metal are incident successively on the metal surface. The ratio of the maximum velocity of photoelectrons emitted in the two cases will be
- (a)
1 : 2
- (b)
2 : 1
- (c)
1 : 4
- (d)
4 : 1
Cut-off potentials for a metal in photoelectric effect for light of wavelength \({ \lambda }_{ 1 },{ \lambda }_{ 2 }\quad and\quad { \lambda }_{ 3 }\) is found to be \({ V }_{ 1 },{ V }_{ 2 }\quad and\quad { V }_{ 3 }\) volt. If \({ V }_{ 1 },{ V }_{ 2 }\quad and\quad { V }_{ 3 }\) are in arithmetic progression, then \({ \lambda }_{ 1 },{ \lambda }_{ 2 }\quad and\quad { \lambda }_{ 3 }\) will be
- (a)
arithmetic progression
- (b)
geometric progression
- (c)
harmonic progression
- (d)
None of the above
Photons with energy 5 eV are incident on a cathode C of a photoelectric cell. The maximum energy of the emitted photoelectrons is 2 eV. When photons of energy 6 eV are incident on C, no photoelectrons will reach the anode A, if the stopping potential of A relative to C is
- (a)
3 V
- (b)
- 3 V
- (c)
- 1 V
- (d)
4 V
In a photoelectric experiment, the collector plate is at 2.0 V with respect to the emitter plate (made of copper \(\phi =4.5eV\)). The emitter is illuminated by a source of monochromatic light of wavelength 200 nm.
- (a)
The minimum kinetic energy of the photoelectrons reaching the collector is 0
- (b)
The maximum kinetic energy of the photoelectrons reaching the collector is 3.7 eV
- (c)
If the polarity of the battery is reversed, then answer to part A will be 0
- (d)
If the polarity of the battery is reversed, then answer to part B will be 1.7 eV
In a photoelectric experiment, the potential difference V that must be maintained between the illuminated surface and the collector so as just to prevent any electron from reaching the collector is determined for different frequencies f of the incident illumination. The graph obtained is shown in figure.
The maximum kinetic energy of the electrons emitted at frequency f1 is
- (a)
h f1
- (b)
\(\frac { { V }_{ 1 } }{ \left( { f }_{ 1 }-{ f }_{ 0 } \right) } \)
- (c)
\(h\left( { f }_{ 1 }-{ f }_{ 0 } \right) \)
- (d)
\(e{ V }_{ 1 }\left( { f }_{ 1 }-{ f }_{ 0 } \right) \)
In a photo emissive cell, with exciting wavelength \(\lambda \), the maximum kinetic energy of electron is K. If the exciting wavelength is changed to \(3\lambda /4\), then the kinetic energy of the fastest emitted electron will be
- (a)
\(\frac{3K}{4}\)
- (b)
\(\frac{4K}{3}\)
- (c)
less than \(\frac{4K}{3}\)
- (d)
greater than \(\frac{4K}{3}\)
The wavelength of radiation showing the phenomenon of photoelectric effect is halved. Choose the correct statement.
- (a)
The maximum velocity of the emitted photoelectrons gets doubled
- (b)
The maximum kinetic energy of the emitted photoelectrons gets doubled
- (c)
The maximum kinetic energy of the emitted photoelectrons gets halved
- (d)
None of the above
The wavelength of a photon needed to remove a proton from a nucleus which is bound to the nucleus with 1 MeV energy is nearly
- (a)
1.2 nm
- (b)
1.2 x 10-3 nm
- (c)
1.2 x 10-6 nm
- (d)
1.2 x 10 nm
If h is Planck's constant in SI system, then the momentum of a photon of wavelength 0.01 \(\dot { A } \) is
- (a)
10-2 h
- (b)
h
- (c)
102 h
- (d)
1012 h
A proton, a neutron, an electron and an \(\alpha \)- particle have same energy. Then, their de-Broglie wavelengths compare as
- (a)
\({ \lambda }_{ p }={ \lambda }_{ n }>{ \lambda }_{ e }>{ \lambda }_{ \alpha }\)
- (b)
\({ \lambda }_{ \alpha }<{ \lambda }_{ p }={ \lambda }_{ n }<{ \lambda }_{ e }\)
- (c)
\({ \lambda }_{ e }<{ \lambda }_{ p }={ \lambda }_{ n }>{ \lambda }_{ \alpha }\)
- (d)
\({ \lambda }_{ e }={ \lambda }_{ p }={ \lambda }_{ n }={ \lambda }_{ \alpha }\)
Light coming from a discharge tube filled with hydrogen falls on the cathode of the photoelectric cell. The work function of the surface of cathode is 4 eV. Which of the following values of the anode voltage with respect to the cathode will likely to make the photo current zero?
- (a)
- 4 V
- (b)
- 6 V
- (c)
- 8 V
- (d)
- 10 V
Consider a beam of electrons (each electron with energy E0) incident on a metal surface kept in an evacuated chamber. Then,
- (a)
no electrons will be emitted as only photons can emit electrons
- (b)
electrons can be emitted but all with an energy, E0
- (c)
electrons can be emitted with any energy, with a maximum of \({ E }_{ 0 }-\phi \) (\(\phi \) is the work function)
- (d)
electrons can be emitted with any energy, with a maximum of E0
10-3 W of 5000 \(\dot { A } \) light is directed on a photoelectric cell. If the current in the cell is 0.16 \(\mu A\), then the percentage of incident photons which produce photoelectrons, is
- (a)
0.4 %
- (b)
0.04 %
- (c)
20 %
- (d)
10 %
Match the following emission phenomenon given in Column I with their meaning given in Column II and select the correct option from the choices given below
| Column I | Column II |
| A. Thermionic emission | 1. When light of suitable frequency illuminates a metal surface, then electrons are emitted from the surface. |
| B. Photoelectric emission | 2. The emission of electrons from the metal surface under the application of strong electric field. |
| C. Field emission | 3. The energy to the free electrons can be given by heating the metal. |
- (a)
A B C 3 2 1 - (b)
A B C 3 1 2 - (c)
A B C 1 2 3 - (d)
A B C 2 1 3
The radiation corresponding to \(3\rightarrow 2\) transition of hydrogen atom falls on a metal surface to produce photoelectrons. These electrons are made to enter a magnetic field of 3 x 10-4 T. If the radius of the largest circular path followed by these electrons is 10.0 mm, the work function of the metal is close to
- (a)
0.8 eV
- (b)
1.6 eV
- (c)
1.8 eV
- (d)
1.1 eV
If a source of power 4 kW produces 1020 photon/s, the radiation belong to a part of the spectrum called
- (a)
X -rays
- (b)
ultraviolet rays
- (c)
microwaves
- (d)
\(\gamma \) - rays
The surface of a metal is illuminated with the light of 400 nm. The kinetic energy of the ejected photoelectrons was found to be 1.68 eV. The work function of the metal is (hc = 1240 eV-nm)
- (a)
3.09 eV
- (b)
1.42 eV
- (c)
151 eV
- (d)
1.68 eV
The time taken by a photoelectron to come out after the photon strikes is approximately
- (a)
10-4 s
- (b)
10-10 s
- (c)
10-16 s
- (d)
10-1 s
A point source causes photoelectric effect from a small metal plate. Which of the following curves may represent the saturation photo current as a function of the distance between the source and the metal?
- (a)
- (b)
- (c)
- (d)
The graph between the energy log E of an electron and its de-Broglie wavelength log \(\lambda \) will be
- (a)
- (b)
- (c)
- (d)
The anode voltage of a photocell kept fixed. The wavelength \(\lambda \) of the light falling on the cathode is gradually changed. The plate current I of photocell varies as follows
- (a)
- (b)
- (c)
- (d)
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