Science (English Medium) Class 12 - CBSE Important Questions

Light of intensity ‘I’ and frequency ‘v’ is incident on a photosensitive surface and causes photoelectric emission. What will be the effect on anode current when (i) the intensity of light is gradually increased. In each case, all other factors remain the same. Explain, giving justification in each case.

Light of intensity ‘I’ and frequency ‘v’ is incident on a photosensitive surface and causes photoelectric emission. What will be the effect on anode current when (ii) the frequency of incident radiation is increased. In each case, all other factors remain the same. Explain, giving justification in each case.

Light of intensity ‘I’ and frequency ‘v’ is incident on a photosensitive surface and causes photoelectric emission. What will be the effect on anode current when the anode potential is increased? In each case, all other factors remain the same. Explain, giving justification in each case.

Show that the wavelength of electromagnetic radiation is equal to the de Broglie wavelength of its quantum (photon).

The following graph shows the variation of photocurrent for a photosensitive metal : 

(a) Identify the variable X on the horizontal axis.

(b) What does the point A on the horizontal axis represent?

(c) Draw this graph for three different values of frequencies of incident radiation v₁, v₂ and v₃ (v₁ > v₂ > v₃) for same intensity.

(d) Draw this graph for three different values of intensities of incident radiation I₁, I₂ and I₃ (I₁ > I₂ > I₃) having same frequency.

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.

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.