Work Function

Q. Hydrogen atom in ground state is excited by a monochromatic radiation of $\lambda =975\stackrel{\circ }{A}$. Number of spectral lines in the resulting spectrum emitted will be

1. 3
2. 2
3. 6
4. 10

Q. When the energy of the incident radiation is increased by 20%, the kinetic energy of the photoelectrons emitted from a metal surface is increased from 0.5 eV to 0.8 eV. The work function of the metal is

1. 1.3 eV
2. 1.5 eV
3. 0.65 eV
4. 1.0 eV

Q. Two identical copper spheres are separated by 1m in vaccum. How many electrons have to be removed from one sphere and added to the other so that they now attract each other with a force of0.9 N

Q. Monochromatic light of wavelength 589 nm is incident from air in a water surface. What are wavelengths frequency and speed of (1) reflected light (2) refracted light? The refractive index of water is 1.33

Q.

The Correct set from the following in which both pairs are in correct order of melting point is:

1. $\mathrm{LiF}>\mathrm{LiCl};\mathrm{NaCl}>\mathrm{MgO}$

2. $\mathrm{LiF}>\mathrm{LiCl};\mathrm{MgO}>\mathrm{NaCl}$

3. $\mathrm{LiCl}>\mathrm{LiF};\mathrm{NaCl}>\mathrm{MgO}$

4. $\mathrm{LiCl}>\mathrm{LiF};\mathrm{MgO}>\mathrm{NaCl}$

Q. 88. A radioactive nucleus of mass m emits a photon of frequrncy v and the nucleus recoils.the recoil energy will be

Q. A photoelectric surface is illuminated successively by monochromatic light of wavelengths $\lambda$ and $\frac{\lambda }{2}$. If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the surface of the material is
($h$ = Plancks constant, $c$ = speed of light)

1. $\frac{hc}{2\lambda }$
2. $\frac{hc}{\lambda }$
3. $\frac{hc}{3\lambda }$
4. $\frac{3hc}{\lambda }$

Q.

Given figure shows few data points in a photo-electric effect experiment for a certain metal. The minimum energy for ejection of electron from its surface is: (Planck’s constant $h=6.62\times {10}^{-34}J.s$)

1. $2.10eV$

2. $2.27eV$

3. $2.59eV$

4. $1.93eV$

Q. A hydrogen atom in its ground state is irradiated by light of wavelength 970 $\mathring{A}$. Taking $\frac{hc}{e}=1.237\times {10}^{-6}eV$ and the ground state energy of hydrogen atom as $-13.6eV$, the number of lines present in the emission spectrum is

Q.

$[\mathrm{Ti}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6{]}^{3+}$ absorbs light of wavelength 498 nm during a d–d transition. The octahedral splitting energy for the above complex is ___________ $\times {10}^{–19}\mathrm{J}$. (Round off to the nearest integer). $\mathrm{h}=6.626\times {10}^{–34}\mathrm{Js};\mathrm{c}=3\times {10}^8{\mathrm{ms}}^{–1}.$

Q.

The electric field at a point associated with a light wave is E = (100 Vm ${}^{-1}$) sin [(3.0 $\times {10}^{15}{s}^{-1}$)t] sin [$(6.0\times {10}^{15}{s}^{-1})t$]. If this light falls on a metal surface having a work function of 2.0 eV, what will be the maximum kinetic energy of the photo electrons ?

Q.

Why energy is inversely proportional to wavelength? Explain it

Q. A hydrogen atom in its ground state absorbs $10.2eV$ of energy. The angular momentum of electron of the hydrogen atom will increase by the value of:

(Given, Planck's constant $=6.6\times {10}^{-34}Js$).

1. $3.15\times {10}^{-34}Js$
2. $1.05\times {10}^{-34}Js$
3. $4.2\times {10}^{-34}Js$
4. $2.10\times {10}^{-34}Js$

Q. The work function of a substance is $4eV$. The longest wavelength of light that can cause photoelectron emission from this substance is approximately.

1. 540 nm
2. 310 nm
3. 220 nm
4. 400 nm

Q.

What is meant by the work function of a metal?

Q. the frequency of ac is doubled , what happens of a) Inductive reactance b)capacitive reactance with frequency of alternating frequency

Q. The energy gap of silicon is 1.14 eV .The maximum wavelength ( in Angstrom) at which silicon will begin absorbing energy is ( Take $hc=12400eV-A^{\circ }$)

Q. 9. In a photo electric experiment, photon of energy5 eV are incident on a metal surface. They liberateelectrons which are just stopped by an electrode at apotential of -3.5V with respect to the metal. The workfunction of the metal in eV is2) 3.53) 1.51)54) 8.5

Q.

Define work function of a metals.

Q.

A cyclotron is opened at an oscillator frequency of $12MHz$ and has a dee radius $R=50cm$. What is the magnitude of the magnetic field needed for a proton to be accelerated in the cyclotron?

Q.

The potential barrier existing across an unbiased p-n junction is 0.2 volt. What minimum kinetic energy a hole should have to diffuse from the p-side to the n-side if (a) the junction is unbiased, (b) the junction is forward-biased at 0.1 volt and (c) the junction is reverse- biased at 0.1 volt ?

Q.

Photons with energy ${\mathrm{E}}_1=4\mathrm{eV}$ and ${\mathrm{E}}_2=2.5\mathrm{eV}$ alternately illuminate the surface of a metal. The ratio of the maximum speeds of the photoelectrons released in the two scenarios is $2$. The metals work function in electron volts is $\_\_\_\_$.

Q. Five elements $A,B,C,D$ and $E$ have work functions $1.2eV,2.4eV,3.6eV,4.8eV$ and $6eV$ respectively. If light of wavelength $4000\stackrel{\circ }{A}$ is allowed to fall on these elements, then photoelectrons are emitted by

1. $A,B$ and $C$
2. $A,B,C,D$ and $E$
3. $A$ and $B$
4. Only $E$

Q. Two circular coils $\text{A}$ and $\text{B}$ of same radius are made from wire of similar materials but the radius of wire $\text{B}$ is twice that of $\text{A}$. The ratio of values of the potential difference across $\text{A}$ and $\text{B}$, such that the magnetic field induction at their centre may be same, will be

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

Q. calculate the mass of a photon with wavelength 3.6 angstrom.

Q. The work function of material (in eV), whose threshold frequency is 3.2 × 1011 Hz would be

Q.

The constant A in the Richardson-Dushman equation for tungsten is $60\times {10}^{4}A{m}^{-2}{K}^{-2}$ The work function of tungsten is 4.5 eV. A tungsten cathode having a surface area $2.0\times {10}^{-5}{m}^2$ is heated by the heater and the temperature becomes constant. Assuming that the cathode radiates like a blackbody, calculate the saturation current due to thermions. Take stefan constant$=6\times {10}^{-8}W{m}^{-2}{K}^{-4}.$ Assume that the termions take only a small fraction of th heat suplied.

Q. The work function for aluminium surface is 4.2 eV and that for sodium surface is 2.0 eV. The two metals were illuminated with appropriate radiations so as to cause photoemission. Then choose the correct statement.

1. Both aluminium and sodium will have the same threshold frequency.
   
2. The threshold frequency of aluminium will be more than that of sodium.
   
3. The threshold frequency of aluminum will be less than that of sodium.
   
4. Cannot say

Q. The maximum velocity of electrons emitted from a metal surface is $v$. What would be the maximum velocity if frequency of the light is increased by a factor of 4?

1. 2$v$
2. > 2$v$
3. < 2$v$
4. between 2$v$ and 4$v$

Q. Actually what is long wavelength limit and short wavelength limit??