Science (English Medium) Class 12 - CBSE Important Questions

A proton and an α -particle are accelerated through the same potential difference. Which one of the two has greater de-Broglie wavelength Justify your answer.

A proton and an α-particle are accelerated through the same potential difference. Which one of the two has less kinetic energy? Justify your answer.

State two important properties of photon which are used to write Einstein’s photoelectric equation.

Define (i) stopping potential and (ii) threshold frequency, using Einstein’s equation and drawing necessary plot between relevant quantities.

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.

A proton and a deuteron are accelerated through the same accelerating potential. Which one of the two has the greater value of de-Broglie wavelength associated with it, and Give reasons to justify your answer.

A proton and a deuteron are accelerated through the same accelerating potential. Which one of the two has less momentum?

Give reasons to justify your answer.

Write its S.I. unit of (intensity of radiation)

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.

An α-particle and a proton are accelerated through the same potential difference. Find the ratio of their de Broglie wavelength.

Radiation of frequency 10¹⁵ Hz is incident on two photosensitive surface P and Q. There is no photoemission from surface P. Photoemission occurs from surface Q but photoelectrons have zero kinetic energy. Explain these observations and find the value of work function for surface Q.

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?