Threshold Frequency

Q. Silver has a work function of $4.7\text{eV}$. When ultraviolet light of wavelength $100\text{nm}$ is incident upon it, a potential of $7.7\text{V}$ is required to stop the photoelectrons from reaching the collector plate. How much potential will be required to stop the photoelectrons when light of wavelength $200\text{nm}$ is incident upon silver?

1. $3.85\text{V}$
2. $1.5\text{V}$
3. $2.35\text{V}$
4. $15.4\text{V}$

Q. In a photocell, with excitation wavelength $\lambda$, the faster electrons has speed $v$. If the excitation wavelength is changed to $3\lambda /4$, the speed of the fastest electron will be

1. $v(3/4{)}^{1/2}$
2. greater than $v(4/3{)}^{1/2}$
3. $v(4/3{)}^{1/2}$
4. less than $v(4/3{)}^{1/2}$

Q. A metal plate is illuminated with light of a certain frequency. Which of the following determine whether or not electrons are ejected?

1. The area of the plate.
2. The intensity of the light.
3. How long the plate is exposed to the light.
4. The material of which the plate is made.

Q. A metal plate is exposed to light of wavelength $\lambda$. It is observed that electrons are ejected from the surface of the plate. When a retarding uniform electric field $E$ is imposed, no electron can move away from the plate farther than a certain distance $d$. Then the threshold wavelength ${\lambda }_0$ for the material of plate is (e is the electronic charge, h is Plank’s constant and $c$ is the speed of light)

1. ${\lambda }_0={(\frac{1}{\lambda }-\frac{hc}{eEd})}^{-1}$
2. ${\lambda }_0={(\frac{1}{\lambda }-\frac{eED}{hc})}^{-1}$
3. ${\lambda }_0=\lambda -\frac{hc}{eEd}$
4. ${\lambda }_0=\lambda -\frac{eEd}{hc}$

Q. The work functions for metals A, B and C are $1.92eV,2.0eV$ and $5.0eV$ respectively. According to Einstein’s equation, the metals which will emit photoelectrons for a radiation of wavelength $4100A^{\circ }$ is/are

1. None
2. A only
3. A and B only
4. All the three metals

Q.

The work function of a photoelectric material is 3.3 eV. The threshold frequency will be equal to

1. $8\times {10}^{4}Hz$

2. $8\times {10}^{56}Hz$

3. $8\times {10}^{10}Hz$

4. $8\times {10}^{14}Hz$

Q. If a photocell is illuminated with a radiation of $1240{\text{A}}^{\circ }$, then stopping potential is found to be $8\text{V}$ . The work function of the emitter and the threshold wavelength are

1. $1\text{eV},5200\stackrel{\circ }{\text{A}}$
2. $2\text{eV},6200\stackrel{\circ }{\text{A}}$
3. $3\text{eV},7200\stackrel{\circ }{\text{A}}$
4. $4\text{eV},4200\stackrel{\circ }{\text{A}}$

Q. A metal plate is exposed to light of wavelength $\lambda$. It is observed that electrons are ejected from the surface of the plate. When a retarding uniform electric field $E$ is imposed, no electron can move away from the plate farther than a certain distance $d$. Then the threshold wavelength ${\lambda }_0$ for the material of plate is (e is the electronic charge, h is Plank’s constant and $c$ is the speed of light)

1. ${\lambda }_0={(\frac{1}{\lambda }-\frac{hc}{eEd})}^{-1}$
2. ${\lambda }_0={(\frac{1}{\lambda }-\frac{eED}{hc})}^{-1}$
3. ${\lambda }_0=\lambda -\frac{hc}{eEd}$
4. ${\lambda }_0=\lambda -\frac{eEd}{hc}$

Q.

The work function for metals A, B and C are respectively 1.92 eV, 2.0 eV and 5 eV. According to Einstein’s equation, the metals which will emit photo electrons for a radiation of wavelength $4100\stackrel{\circ }{A}$ is/are

1. None of these

2. A only

3. A and B only

4. All the three metals