Science (English Medium) कक्षा १२ - CBSE Important Questions for Physics

The work function of the following metals is given : Na 2.75 ev, K = 2.3 eV, Mo = 4.17 eV and Ni = 5.15 eV. Which of these metals will not cause photoelectric emission for radiation of wavelength 3300 Å from a laser source placed 1 m away from these metals? What happens if the laser source is brought nearer and placed 50 cm away?

A electron of mass me revolves around a nucleus of charge +Ze. Show that it behaves like a tiny magnetic dipole. Hence prove that the magnetic moment associated wit it is expressed as `vecμ =−e/(2 m_e)vecL `, where `vec L` is the orbital angular momentum of the electron. Give the significance of negative sign.

A photosensitive surface emits photoelectrons when red light falls on it. Will the surface emit photoelectrons when blue light is incident on it? Give reason. 

Draw a plot showing the variation of photoelectric current with collector potential for different frequencies but same intensity of incident radiation ?

Use Einstein's photoelectric equation to explain the observations from this graph ?

What change will you observe if intensity of incident radiation is changed but the frequency remains the same?

Plot a graph showing the variation of photoelectric current with intensity of light. The work function for the following metals is given:
Na: 2.75 eV and Mo : 4.175 eV.
Which of these will not give photoelectron emission from a radiation of wavelength 3300

\[A^\circ\] from a laser beam? What happens if the source of laser beam is brought closer?

Define the term "cut off frequency" in photoelectric emission. The threshod frequency of a metal is f. When the light of frequency 2f is incident on the metal plate, the maximum velocity of photo-electrons is v₁. When the frequency of the incident radiation is increased to 5f, the maximum velocity of phto-electrons is v₂. Find the ratio v₁ : v₂.

A beam of monochromatic radiation is incident on a photosensitive surface. Answer the following question giving reason :

Do the emitted photoelectrons have the same kinetic energy?

A beam of monochromatic radiation is incident on a photosensitive surface. Answer the following question giving reason :

Does the kinetic energy of the emitted electrons depend on the intensity of incident radiation?

A beam of monochromatic radiation is incident on a photosensitive surface. Answer the following question giving reason :

On what factors does the number of emitted photoelectrons depend?

Plot a graph showing the variation of photoelectric current with collector plate potential at a given frequency but for two different intensities I₁ and I₂, where I₂ > I₁.

In photoelectric effect, why should the photoelectric current increase as the intensity of monochromatic radiation incident on a photosensitive surface is increased? Explain.

Define the term ‘stopping potential’ in relation to photo-electric effect.

Draw a plot showing the variation of photoelectric current with collector plate potential for two different frequencies, v₁ > v₂, of incident radiation having the same intensity. In which case will the stopping potential be higher? Justify your answer.

Use Einstein’s photoelectric equation to show how from this graph, 
(i) Threshold frequency, and (ii) Planck’s constant can be determined.

Work function of aluminium is 4.2 eV. If two photons each of energy 2.5 eV are incident on its surface, will  the emission of electrons take place? Justify your answer. 

Define the term "Threshold frequency", in the context of photoelectric emission.  

Define the term: threshold frequency

Answer the following question.
Plot a graph of photocurrent versus anode potential for radiation of frequency ν and intensities I₁ and I₂ (I₁ < I₂).