The Photon Model

Q.

A p-n photodiode is fabricated from a semiconductor with band gap of 2.8 eV. Can it detect a wavelength of 6000 nm?

Q.

The frequency and intensity of a light source are both doubled. Consider the following statements.

A. The saturation photocurrent remains almost the same

B. The maximum kinetic energy of the photoelectrons is doubled

1. A is false but B is true

2. Both A and B are true

3. Both A and B are false

4. A is true but B is false

Q. When a certain photosensitive surface is illuminated with monochromatic light of wavelength $\lambda$, the stopping potential for photoelectric current is $2V_0$. When the same surface is illuminated with monochromatic light of wavelength $2\lambda$, the stopping potential is $\frac{V_0}{2}$. The threshold wavelength for photoelectric emission is

1. $2.5\lambda$
2. $3\lambda$
3. $2.0\lambda$
4. $1.5\lambda$

Q.

When radiation of wavelength $\lambda$is incident on a metallic surface, the stopping potential is 4.8 volts. If the same surface is illuminated with radiation of double the wavelength, then the stopping potential becomes 1.6 volts. Then the threshold wavelength for the surface is

1. $4\lambda$

2. $2\lambda$

3. $6\lambda$

4. $8\lambda$

Q.

Photoelectric effect supports quantum nature of light because

1. There is a minimum frequency below which no photoelectrons are emitted

2. The maximum kinetic energy of photoelectrons depends only on the frequency of light and not on its intensity

3. Even when the metal surface is faintly illuminated the photoelectrons leave the surface immediately

4. Electric charge of the photoelectrons is quantized.

Q.

(a) For what kinetic energy of a neutron will the associated de Broglie wavelength be 1.40 × 10⁻¹⁰ m?

(b) Also find the de Broglie wavelength of a neutron, in thermal equilibrium with matter, having an average kinetic energy of (3/2) kT at 300 K.

Q.

The energy of a photon of light of wavelength 450 nm is

1. $2.5\times {10}^{-19}J$

2. $4.4\times {10}^{-19}J$

3. $1.25\times {10}^{-17}J$

4. $2.5\times {10}^{-17}J$

Q.

What is the change ln wavelength & velocity when light travells phically rarer to denser medium?

Q. In $L{i}^{++}$ electron in first Bohr orbit is excited to a level by a radiation of wavelength $X$. When the ion gets deexcited to the ground state in all possible ways (including intermediate emissions), a total of six spectral lines are observed. What is the value of $\lambda$ ?

1. $11.4\text{nm}$
2. $12.3\text{nm}$
3. $10.8\text{nm}$
4. $9.4\text{nm}$

Q.

The energy of a photon of light with wavelength $5000\stackrel{\circ }{A}$ is approximately 2.5 eV. This way the energy of an X-ray photon with wavelength $1\stackrel{\circ }{A}$ would be

1. $\frac{2.5}{5000eV}$

2. $\frac{2.5}{(5000{)}^{2}eV}$

3. $2.5\times 5000eV$

4. $2.5\times (5000{)}^{2}eV$

Q. An excited $H{e}^{+}$ ion emits two photons in succession, with wavelengths $108.5\text{nm}$ and $30.4\text{nm}$, in making a transition to ground state. The quantum number $n$, corresponding to its initial excited is (for photon of wavelength $\lambda$ energy $E=\frac{1240\text{eV}}{\lambda \text{(in nm)}}$

1. $n=5$
2. $n=4$
3. $n=7$
4. $n=6$

Q. Define intensity of radiation on the basis of photon picture of light. Write its S.I. unit

Q.

The principle of laser action involves

1. Amplification of particular frequency emitted by the system

2. Population inversion

3. Stimulated emission

4. All of the above

Q.

Which alkali metal does not exhibit photoelectric effect_______.

Q. Find the (a) maximum frequency, and (b) minimum wavelength of X-rays produced by 30 kV electrons.

Q. A 100W sodium lamp radiates energy uniformly in all directions. The lamp is located at the centre of a large sphere that absorbs all the sodium light which is incident on it. The wavelength of the sodium light is 589 nm. (a) What is the energy per photon associated with the sodium light? (b) At what rate are the photons delivered to the sphere?

Q. Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW. (a) Find the energy and momentum of each photon in the light beam, (b) How many photons per second, on the average, arrive at a target irradiated by this beam? (Assume the beam to have uniform cross-section which is less than the target area), and (c) How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon?

Q.

Light of wavelength $0.6\mu m$ from a sodium lamp falls on a photo cell and causes the emission of photoelectrons for which the stopping potential is 0.5V with light of wavelength $0.4\mu m$ from a sodium lamp, the stopping potential is 1.5V, with this data the value of $\frac{h}{e}$is:

1. $4\times {10}^{-19}V.s$

2. $4\times {10}^{-15}V.s$

3. $0.25\times {10}^{-15}V.s$

4. $4\times {10}^{-8}V.s$

Q.

Who discovered the photoelectric effect?

Q. In a photoelectric experiment a parallel beam of monochromatic light with power of $200$ W is incident on a perfectly absorbing cathode of work function $6.25$ eV. The frequency of light is just above the threshold frequency so that the photoelectrons are emitted with negligible kinetic energy. Assume that the photoelectron emission efficiency is $100\%.$ A potential difference of $500$ V is applied between the cathode and the anode. All the emitted electrons are incident normally on the anode and are absorbed. The anode experiences a force $F=n\times {10}^{-4}\text{N}$ due to the impact of the electrons. The value of $n$ is . Mass of the electron $m_e=9\times {10}^{-31}\text{kg}$ and $1.0\text{eV}=1.6\times {10}^{-19}\text{J}.$

Q. What is the momentum of photon of energy 3 MeV in $kgm{s}^{-1}$?

1. $9\times {10}^{-21}$
2. $1.6\times {10}^{-21}$
3. $9\times {10}^{-28}$
4. $3\times {10}^{-28}$

Q. The wavelength of a red light is 700 nm. The energy contained in each photon of light is.

1. 4.77 eV
2. 3.77 eV
3. 2.77 eV
4. 1.77 eV

Q. We may state that the energy E of a photon of frequency v is E = hv where h is a Planck’s constant. The momentum P of a photon is $P=\frac{h}{\lambda }$ where $\lambda$ is the wavelength of the photon. From the above statement one may conclude that the wave velocity of light is equal to

1. $4\times {10}^{5}m{s}^{-1}$
2. $\frac{E}{p}$
3. $Ep$
4. ${\left(\frac{E}{p}\right)}^2$
   
   

Q. Wavelength of light of frequency $100$ $Hz$ is,

1. $4\times {10}^{6}m$
2. $3\times {10}^{6}m$
3. $2\times {10}^{6}m$
4. $5\times {10}^{-5}m$

Q.

Polarisation of light proves the

1. Corpuscular nature of light

2. Longitudinal nature of light

3. Quantum nature of light

4. Transverse nature of light

Q.

A beam of white light is incident normally on a plane surface absorbing 70$\%$ of the light and reflecting the rest. If the incident beam carries 10 W of power, find the force exerted by it on the surface.

Q. Light of wavelength $5000\stackrel{\circ }{A}$ is falling on a photo sensitive surface. If the surface has received ${10}^{-7}$J of energy, then the number of photons falling on the surface will be

1. $5\times {10}^{11}$
2. $9\times {10}^{11}$
3. $2.5\times {10}^{11}$
4. $1\times {10}^{11}$

Q. The approximate wavelength of a photon of energy 2.48 eV is

1. $500\dot{A}$
2. $5000\dot{A}$
3. $2000\dot{A}$
4. $1000\dot{A}$

Q. Name the phenomenon which shows the quantum nature of electromagnetic radiation.

Q. The energy flux of sunlight reaching the surface of the earth is 1.388 × 103 W/m2 . How many photons (nearly) per square metre are incident on the Earth per second? Assume that the photons in the sunlight have an average wavelength of 550 nm.