Stopping Potential Revisited

Q. The work function of metal is 1 eV. Light of wavelength 3000 Å is incident on this metal surface. The velocity of emitted photo-electrons will be

1. $1\times {10}^{6}m/sec$

2. 10 m/sec

3. $1\times {10}^{3}m/sec$

4. $1\times {10}^{4}m/sec$

Q. A metal surface of work function 1.07 eV is irradiated with light of wavelength 332 nm. The retarding potential required to stop the escape of photoelectrons is

1. 4.81 eV

2. 3.74 eV

3. 1.07 eV
4. 2.66 eV

Q.

In a photoelectric effect experiment, the graph of stopping potential V versus reciprocal of wavelength obtained is shown in the figure. As the intensity of incident radiation is increased:

1. Straight line shifts to right

2. Straight line shifts to left

3. Slope of the straight line get more steep

4. Graph does not change

Q.

The maximum wavelength of radiation that can produce photoelectric effect in a certain metal is 200 nm. The maximum kinetic energy acquired by electron due to radiation of wavelength 100 nm will be

1. 6.2 eV

2. 12.4 eV

3. 100 eV

4. 200 eV

Q.

Sodium and copper have work functions 2.3eV and 4.5eVrespectively. Then the ratio of their threshold wavelengths is nearest to

1. 1 : 2

2. 4 : 1

3. 2 : 1

4. 1 : 4

Q. In a photoelectric experiment for 4000 Å incident radiation, the potential difference to stop the ejection is 2 V. If the incident light is changed to 3000 Å, then the potential required to stop the ejection of electrons will be

1. 2 V
2. Less than 2 V
3. Zero
4. Greater than 2 V

Q. The light of two different frequencies whose photons have energies $3.8\text{eV}$ and $1.4\text{eV}$ respectively, illuminate a metallic surface whose work function is $0.6\text{eV}$ successively. The ratio of maximum speeds of emitted electrons for the two frequencies respectively will be

1. $1:1$
2. $4:1$
3. $2:1$
4. $1:4$

Q. Light of wavelength 4000 Å is incident on a sodium surface for which the threshold wave length of photo – electrons is 5420 Å. The work function of sodium is

1. 0.57 eV

2. 2.29 eV

3. 1.14 eV

4. 4.58 eV

Q. Threshold wavelength for photoelectric effect on sodium is 5000 Å. Its work function is

1. 15 J
2. $16\times {10}^{-14}J$
3. $4\times {10}^{-81}J$
4. $4\times {10}^{-19}J$

Q.

Light of wavelength $\lambda$ strikes a photo-sensitive surface and electrons are ejected with kinetic energy E. If the kinetic energy is to be increased to 2E, the wavelength must be changed to ${\lambda }^{\prime }$ where

1. ${\lambda }^{\prime }=2\lambda$

2. $\frac{\lambda }{2}<{\lambda }^{\prime }<\lambda$

3. ${\lambda }^{\prime }=\frac{\lambda }{2}$

4. ${\lambda }^{\prime }>\lambda$

Q.

Light incident normally on a plane mirror attached to a galvanometer coil retraces backwards as shown in Fig. 9.36. A current in the coil produces a deflection of 3.5° of the mirror. What is the displacement of the reflected spot of light on a screen placed 1.5 m away?

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.

Q. The surface of certain metal is first illuminated with light of wavelength ${\lambda }_1=350\text{nm}$ and then, by light of wavelength ${\lambda }_2=540\text{nm}$. It is found that the maximum speed of the photo electrons in the two cases differ by a factor of $2$. The work function of the metal $\text{(in eV)}$ is close to:
$\text{(Energy of photon}=\frac{1240}{\lambda \left(\text{in nm}\right)}\text{eV})$

1. $5.6$
2. $1.8$
3. $2.5$
4. $1.4$

Q.

If the energy of a photon corresponding to a wavelength of $6000\stackrel{\circ }{A}is3.32\times {10}^{-19}J$, the photon energy for a wavelength of $4000\stackrel{\circ }{A}$ will be

1. 1.4 eV

2. 4.9 eV

3. 3.1 eV

4. 1.6 eV

Q.

The work functions of metals A and B are in the ratio 1 : 2. If light of frequencies fand 2fare 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)

1. 1 : 3

2. 1 : 1

3. 1 : 2

4. 1 : 4

Q.

Two identical metal plates show photoelectric effect by a light of wavelength ${\lambda }_A$ falls on plate A and ${\lambda }_B$ on plate B $({\lambda }_A=2{\lambda }_B)$. The maximum kinetic energy is

1. $2K_A=K_B$

2. $K_A<\frac{K_B}{2}$

3. $K_A=2K_B$

4. $K_A=\frac{K_B}{2}$

Q.

Light of wavelength 5000 $\stackrel{\circ }{A}$ falls on a sensitive plate with photoelectric work function of 1.9 eV. The kinetic energy of the photoelectron emitted will be

1. 0.58 eV

2. 2.48 eV

3. 1.24 eV

4. 1.16 eV

Q.

A monochromatic light source of intensity 5 mW emits 8 $\times {10}^{15}$ photons per second. This light ejects photo electrons from a metal surface. The stopping potential for this setup is 2.0 V. Calculate the work function of the metal.

Q. If $m$ is the mass of an electron and $c$ is the speed of light, the ratio of the wavelength of a photon of energy $E$ to that of the electron of the same energy is,

1. $c\sqrt{\frac{2m}{E}}$
2. $\sqrt{\frac{2m}{E}}$
3. $\sqrt{\frac{2m}{cE}}$
4. $\sqrt{\frac{m}{E}}$

Q. A source of 30W illuminates the cathode of a photocell with radiation of wavelength 6600angrastom.The saturation current will be (efficiency of photoelectric emission is 1%)

Q. The photoelectric threshold wavelength for a metal surface is $6600\stackrel{\circ }{A}$ . The work function for this is

1. 1.87 V
2. 0.18 eV
3. 18.7 eV
4. 1.87 eV

Q.

The photoelectric work function for a metal surface is 4.125 eV. The cut-off wavelength for this surface is

1. $4125\stackrel{\circ }{A}$

2. $2062.5\stackrel{\circ }{A}$

3. $3000\stackrel{\circ }{A}$

4. $6000\stackrel{\circ }{A}$

Q.

In a p-n junction, the depletion region is 400 nm wide and an electric field of $5\times {10}^{5}V{m}^{-1}$ exists in it. (a) Find the height of the potential barrier. (b) What should be the minimum kinetic energy of a conduction electron which can diffuse from the n-side to the p-side ?

Q.

In photoelectric effect stopping potential is $3V_0$ for incident wavelength ${\lambda }_0$ and stopping potential for incident wavelength$2{\lambda }_0$. Find threshold wavelength.

1. $3{\lambda }_0$

2. $2{\lambda }_0$

3. $4{\lambda }_0$

4. $8\lambda$

Q.

Light of wavelength $1824\stackrel{\circ }{A}$, incident on the surface of a metal, produces photo-electrons with maximum energy 5.3 eV. When light of wavelength $1216\stackrel{\circ }{A}$ is used, the maximum energy of photoelectrons is 8.7 eV. The work function of the metal surface is

1. 13.6 eV

2. 6.8 eV

3. 3.5 eV

4. 1.5 eV

Q.

Stopping potential for photoelectrons

1. Depends on both the frequency of the incident light and nature of the cathode material

2. Depends upon the intensity of the incident light
3. Does not depend on the frequency of the incident light

4. Does not depend upon the nature of the cathode material

Q.

How many photons are emitted by a laser source $5\times {10}^{-3}W$ operating at $632.2nm$ in $2s$?

1. $3.2\times {10}^{16}$

2. $1.6\times {10}^{16}$

3. $4\times {10}^{16}$

4. None of these

Q. When radiation is incident on a photoelectron emitter, the stopping potential is found to be 9 volts. If e/m for the electron is $1.8\times {10}^{11}Ck{g}^{-1}$ the maximum velocity of the ejected electrons is

1. $6\times {10}^{5}m{s}^{-1}$
2. $1.8\times {10}^{5}m{s}^{-1}$
3. $8\times {10}^{5}m{s}^{-1}$
4. $1.8\times {10}^{6}m{s}^{-1}$

Q.

Threshold frequency for a metal is ${10}^{15}Hz$. Light of $\lambda =4000\stackrel{\circ }{A}$ falls on its surface. Which of the following statements is correct

1. No photoelectric emission takes place

2. Photo-electrons come out with zero speed

3. Photo-electrons come out with ${10}^5$ m/sec speed

4. Photo-electrons come out with ${10}^3$ m/sec speed
   

Q.

What happens to ejected photoelectrons KE if the wavelength of incident light decreases?